Customer Development Interviews: A Practical Guide

Customer development interviews are one of the most valuable activities a startup founder can do. Direct conversations with customers and potential customers reveal insights that no amount of analytics or survey data can provide. Yet most founders either don't do enough of them or do them in ways that don't yield useful information.

This article shares our approach to customer interviews based on hundreds of conversations across our portfolio companies.

Why Most Customer Interviews Fail

Asking Leading Questions

"Wouldn't it be great if the product could do X?" Of course they'll say yes—you've led them to the answer. Leading questions confirm your biases rather than revealing truth.

Talking About the Future

"Would you use a product that...?" People are terrible at predicting their own behavior. What they say they'll do and what they actually do often differ dramatically.

Pitching Instead of Listening

Founders love their products and want to talk about them. But interviews are for listening, not selling. Every minute you spend talking is a minute you're not learning.

Asking for Opinions Instead of Facts

"What do you think of...?" gives you opinions. "Tell me about the last time you..." gives you facts about actual behavior.

The Mom Test

Rob Fitzpatrick's "Mom Test" provides a useful framework. The idea: ask questions that even your mom (who wants to be supportive) can't lie to you about. This means:

Talk about their life, not your idea
Ask about specifics in the past, not generics or opinions about the future
Talk less, listen more

Instead of "Would you use a product like this?" ask "How do you currently handle this problem?" Instead of "What would you pay for this?" ask "How much do you spend on solving this now?"

Preparing for Interviews

Know Your Hypotheses

We recommend that every interview test specific hypotheses. What do you believe? What would change your mind? Write these down before you start.

Prepare Questions

Have a list of questions, but be prepared to deviate. The best interviews are conversations, not interrogations. Good questions:

Tell me about the last time you encountered [problem]...
Walk me through how you currently handle...
What's the hardest part of...
Why do you do it that way?
What have you tried before?

Target the Right People

Talk to people who actually have the problem you're solving, in the context you're solving it. Your friends and family are rarely the right people to interview unless they happen to be your target market.

During the Interview

Build Rapport First

People open up more when they're comfortable. Spend a few minutes on small talk before diving into questions.

Let Them Talk

Your job is to ask questions and listen. Resist the urge to fill silence—people often say the most interesting things after a pause.

Follow the Energy

When someone gets animated or emotional about a topic, dig deeper. That's where the real insights often lie.

Ask "Why" (Gently)

Understanding the reasoning behind behavior is often more valuable than knowing the behavior itself. But ask "why" gently—it can feel confrontational.

Take Notes

Record interviews if you can get permission, and take notes regardless. You'll forget important details otherwise.

After the Interview

Debrief Immediately

Write up your key takeaways right after the interview while details are fresh. What surprised you? What confirmed your hypotheses? What challenged them?

Look for Patterns

We've learned that single interviews can be misleading. Look for patterns across multiple conversations. Consistent themes across 5-10 interviews are much more reliable than insights from one conversation.

Update Your Hypotheses

The point of interviews is to learn. If your hypotheses don't evolve based on what you hear, you're either right (rare) or not actually listening.

How Many Interviews?

There's no magic number, but general guidance:

For problem validation: 15-20 interviews
For solution validation: 10-15 interviews
For ongoing learning: Regular cadence (e.g., 2-3 per week)

You know you've done enough when you stop hearing new information—the same themes and patterns emerge repeatedly.

Beyond Interviews

Interviews are powerful but not sufficient. Complement them with:

Observation: Watch customers use your product or handle the problem you solve
Analytics: Quantitative data on actual behavior
Support conversations: What are customers asking about?
Sales conversations: What objections come up?

Conclusion

Customer development interviews are high-leverage activities that most startups underinvest in. A few hours of good customer conversations can prevent months of building the wrong thing.

The key is doing them right: asking about past behavior rather than future intentions, listening more than talking, and being open to having your assumptions challenged. Make customer interviews a regular part of your startup routine, not a one-time activity.