How to Choose a B2B Lead Generation Agency (Without Getting Burned)

Most agencies say the right things on the sales call. The difference between the agencies that actually deliver and the ones that do not is usually invisible until you have signed a three-month contract.

They will tell you they have proprietary systems. They will show you case studies with impressive numbers. They will promise meetings, pipeline, and revenue. They will make it sound like signing with them is the obvious decision.

The difference between the agencies that actually deliver and the ones that do not is usually invisible until you have signed a three-month contract, paid your first invoice, and waited six weeks for results that never arrive.

I run a B2B lead generation agency. I know what good looks like from the inside. I also know what bad looks like, because I have seen the wreckage that clients bring to us after working with agencies that overpromised and underdelivered.

So here is what I would ask if I were evaluating an agency. These are the questions that separate the operators who know what they are doing from the ones who are selling a service they cannot fulfil.

What to Ask About Infrastructure

Cold email infrastructure is the foundation that everything else sits on. If the infrastructure is wrong, nothing else matters. The best script in the world will not generate replies if your emails are landing in spam.

Here are the questions you should ask:

"How many inboxes will you set up for my campaigns?"

A serious cold email operation uses dedicated inboxes, typically 100 or more per client for campaigns at scale. Each inbox sends a limited number of emails per day (up to 15, ramped up gradually) to maintain deliverability. If an agency is vague about inbox numbers or says they will "use a few email accounts," that tells you they do not understand the infrastructure required.

"Who provides your inboxes and what type are they?"

There is a meaningful difference between standard inboxes and premium inboxes. Premium inboxes from established providers come with better domain reputation and higher deliverability out of the box. If the agency is buying the cheapest inboxes available or using their own domains for multiple clients, your deliverability will suffer.

"How long is your warmup period?"

New inboxes need to be warmed up before they can send at volume. This typically takes two to four weeks. An agency that skips warmup or rushes it is gambling with your deliverability. If they tell you campaigns will be live within days of signing, ask how they plan to warm inboxes that quickly. If they cannot explain the process, that is a problem.

"How many domains will you use?"

Your primary business domain should never be used for cold email. A proper setup uses secondary domains (variations of your main domain) to protect your brand's email reputation. Expect three to five domains minimum, each with multiple inboxes. If an agency plans to send from your main domain, walk away. If your main domain gets flagged for spam, your regular business emails stop reaching people too.

Why These Questions Matter

Infrastructure questions are the fastest way to identify whether an agency actually operates campaigns or simply resells someone else's service. An agency that runs real infrastructure will answer these questions immediately, with specific numbers and provider names. An agency that does not will deflect, give vague answers, or change the subject to talk about their "proprietary technology."

If they cannot answer specifically, that is your first red flag.

What to Ask About Targeting

Targeting is where campaigns succeed or fail. The best infrastructure and the best scripts will not generate results if you are reaching the wrong people. This is the area where most agencies cut corners because proper targeting is time-intensive.

"How do you build lists? What databases do you use?"

You want specifics. Which data providers? How do they verify email addresses? What enrichment tools do they use to fill in missing data? A good agency will name their tools and explain their process. A weaker agency will say something like "we have access to millions of contacts" without explaining where those contacts come from or how they verify accuracy.

"Do you build separate campaigns per segment?"

This is a critical question. Sending the same email to a 10-person startup founder and a 500-person enterprise VP is a mistake. Different segments have different pain points, different language, and different decision-making processes. Your agency should be building distinct campaigns for distinct segments, each with tailored messaging.

If they tell you they run one campaign for your entire ICP, that is a sign they are optimising for their own efficiency, not your results.

"Can I see and approve lists before they go out?"

You should always have visibility into who is being contacted on your behalf. These people will associate the outreach with your brand. If your agency is emailing the wrong people, the wrong titles, or the wrong company sizes, that reflects on you.

An agency that resists showing you lists is either cutting corners on targeting or worried you will spot problems. Either way, you want transparency here.

"How do you handle list exhaustion?"

Every market has a finite number of prospects. What happens when your agency has emailed everyone in your ICP? Do they retarget with fresh messaging? Expand into adjacent segments? Adjust the criteria? This question tells you whether the agency thinks beyond the first month of campaigns.

What to Ask About Scripts

The emails your agency sends are the words your prospects read. They represent your business, your offer, and your professionalism. You should care deeply about what they say.

"Can I see scripts before they go out?"

This should be non-negotiable. You should review and approve every email script before it reaches a single prospect. Any agency that pushes back on this is prioritising their convenience over your brand.

That said, be careful about the inverse problem: rewriting scripts to add corporate jargon, buzzwords, or marketing language that sounds good internally but performs poorly in cold outreach. The best agencies will push back on changes that hurt performance, and that pushback is a good sign.

"How long are your emails?"

Cold emails should be short. Genuinely short. The first email in a sequence should be 50-100 words. Follow-ups can be even shorter. If an agency shows you email templates that read like marketing brochures with multiple paragraphs, bullet points, and calls to action, they do not understand cold email.

Your prospect is scanning their inbox. They will give your email five seconds. If they cannot understand who you are, why you are reaching out, and what you want them to do in those five seconds, the email fails.

"Do you A/B test?"

Every campaign should be testing variables: subject lines, opening lines, offers, calls to action. A/B testing is how you improve performance over time. An agency that sends the same script for three months without testing anything is leaving results on the table.

Ask specifically: what do you test, how often, and how do you decide what changes to make? You want to hear a systematic process, not "we change things when they're not working."

"How do you develop scripts? What's your research process?"

The quality of a cold email script depends entirely on the quality of the research behind it. How does the agency learn about your market? Your prospects' pain points? Your competitive advantages? Do they interview you extensively, or do they write generic templates and swap in your company name?

A thorough agency will have a structured research process that takes hours, not minutes. They should be asking you detailed questions about your clients, your market, your competitors, and what makes prospects say yes.

What to Ask About Campaign Management

Once campaigns are live, someone has to manage them. This is where the day-to-day experience of working with an agency is defined.

"How many clients does each campaign manager handle?"

This is perhaps the most revealing question you can ask. An account manager handling five clients can give each one meaningful attention. An account manager handling twenty clients is checking dashboards and hoping nothing breaks.

Ask directly. If they will not answer, assume the number is too high for them to admit.

"How quickly do you respond to prospect replies?"

When a prospect replies to your cold email expressing interest, the clock starts. Research consistently shows that responding within five minutes dramatically increases the probability of booking a meeting compared to responding within an hour. Within an hour is dramatically better than within a day.

Ask the agency what their target response time is. Then ask what their actual average response time is. These are often very different numbers.

"Do you do warm calling on engaged prospects?"

This separates the top tier of agencies from the rest. Email generates interest. Phone calls convert that interest into meetings. An agency that only sends emails is leaving conversions on the table.

Ask whether they call prospects who open emails multiple times, click links, or send non-committal replies. If they do, ask who makes the calls and what training they have had. A good warm caller can double the meeting output of an email-only campaign.

"What does reporting look like?"

You should receive regular reports that go beyond vanity metrics. What you actually need to see:

• Emails sent per period
• Reply rates (total and positive)
• Meetings booked
• Campaign-by-campaign performance
• What changes were made and why
• What the plan is for the next period

If an agency sends you a dashboard link and expects you to interpret it yourself, that is not reporting. That is data. Reporting includes analysis, interpretation, and recommended next steps.

What to Ask About Results

This is where every agency sounds confident. The questions below help you separate confidence from competence.

"Can I speak to a current client?"

Not a testimonial. Not a case study. A real conversation with someone who is currently paying the agency and receiving their service right now.

Past clients can give positive references for all sorts of reasons. Current clients will tell you what the actual experience is like: response times, communication quality, results consistency, and whether the agency does what they said they would do.

If an agency cannot connect you with a single current client willing to speak on their behalf, ask yourself why.

"What happens if campaigns underperform?"

This is the question most prospects forget to ask. Everything sounds great when the agency is pitching you. But what happens in month two when reply rates are below expectations?

Do they adjust scripts? Rebuild lists? Change the approach? Or do they tell you to "be patient" and wait it out? You want to hear a specific process for diagnosing and fixing underperformance, not just reassurance that it will not happen.

"What is the total cost, and what is the commitment?"

Get the full picture. Monthly retainer, setup fees, infrastructure costs, minimum commitment period. Some agencies quote a low monthly fee but charge separately for inboxes, domains, data, and tools. Others include everything in one price.

Neither model is inherently better, but you need to understand the total cost before you sign. A three-month minimum commitment at three thousand euros per month is a nine-thousand-euro decision. Treat it like one.

"What does the onboarding process look like?"

How long from contract signing to first emails sent? What do they need from you? How much of your time will the onboarding require? A structured onboarding process with clear timelines and deliverables is a sign of operational maturity. "We'll get started and figure it out as we go" is not.

Red Flags That Should Stop the Conversation

Some signals should end your evaluation immediately. Not because the agency is necessarily dishonest, but because these patterns consistently correlate with poor outcomes.

Guaranteed Results Before Understanding Your Business

Any agency that guarantees a specific number of meetings or leads before understanding your ICP, your market, your offer, and your competitive landscape is making a promise they cannot keep. Results in cold outreach depend on dozens of variables, many of which are specific to your business. Guarantees before discovery are a sales tactic, not a commitment.

No Infrastructure Specifics

If the agency cannot tell you exactly how many inboxes, domains, and what sending platform they use, they either do not manage infrastructure themselves or do not understand why it matters. Both are problems.

No Script Approval Process

If you cannot see and approve the emails being sent on your behalf, you have no control over how your brand is represented to thousands of prospects. This is not a negotiable point.

One-Size-Fits-All Approach

Every client's market is different. Every ICP has different pain points. Every offer requires different positioning. An agency that uses the same scripts, the same targeting approach, and the same campaign structure for every client is optimising for their own operational efficiency at the expense of your results.

Unable to Provide Current Client References

This is the single most telling red flag. An agency that delivers results has clients who are happy to say so. An agency that cannot produce a single current reference either does not have happy clients or does not have clients at all.

Reluctance to Explain Their Process

Good agencies are proud of their process. They will walk you through exactly how they build lists, write scripts, manage campaigns, and handle replies. If an agency treats their process as a "secret sauce" they cannot share, they are usually hiding the fact that there is no real process to share.

The Bottom Line

Choosing a lead generation agency is not about finding the one with the best pitch or the most impressive website. It is about finding the one that can answer hard questions with specific answers.

The questions in this article are not designed to trip agencies up. They are designed to identify the ones that actually know what they are doing. An agency that welcomes these questions is one that has invested in building a real operation. An agency that deflects them is one you should avoid.

Your investment in a lead generation agency is not just financial. It is reputational. Every email sent on your behalf carries your name. Every phone call made represents your business. Choose the agency that takes that responsibility as seriously as you do.

How We Handle These Questions at Sparklead

We answer all of the questions in this article on our strategy calls, openly and specifically. We will tell you exactly how many inboxes we use, how we build lists, how we write scripts, and what our management process looks like. We will connect you with current clients. We will show you real campaign data.

If you are evaluating lead generation agencies and want a conversation with one that welcomes hard questions, book a strategy call.