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Customer interview questions: 30 that get the truth, by stage

By Tudor Bungardean. Published 12 October 2026. Every outside fact read on 12 October 2026.

Good customer interview questions ask about what the person did, not what they would do: the last time the problem happened, what they tried, what it cost them, and what they did next. The thirty questions below follow the three rules Rob Fitzpatrick set out in The Mom Test: talk about their life instead of your idea, ask about specific past events instead of hypotheticals, and talk less than they do. They run in five stages, from the problem to the commitment, so an interview that stops early still tells you something.

The three rules, before the questions

  • Talk about their life, not your idea. The moment you describe the product, the answers become politeness.
  • Ask about specific events in the past, never about the future. “Would you use this” has no wrong answer; “when did this last happen” has one.
  • Talk less and listen more. If you are speaking more than a fifth of the time, you are pitching.
  • A compliment is not data. Five interviews that end in a concrete next step outweigh fifty that end in “sounds great”.

Stage 1: the problem, as it actually happens

  • Tell me about the last time [the problem] came up. Start from the beginning.
  • How often does that happen? When was the time before that?
  • What was the worst version of it this year?
  • Who else was involved, or affected, when it happened?
  • What did it stop you from doing that day?
  • What did you do about it in the end?

Stage 2: the current solution

  • Walk me through how you handle it today, step by step.
  • What tools or people are part of that? How did you choose them?
  • What have you tried before that you stopped using? Why did you stop?
  • What do you like about how you do it now?
  • Where does it break, and how do you find out it broke?
  • If it disappeared tomorrow, what would you do?

Stage 3: money and time

  • What do you pay today for anything in this area, including people’s time?
  • How did that spend get approved, and by whom?
  • How many hours a week does it take you, or someone you pay?
  • What did the last mistake in this area cost, in money or in a customer?
  • When did you last buy something to fix a problem like this? What made you do it then?
  • What is the budget this would come out of?

Stage 4: the trigger

  • What has changed recently that made this worse, or more urgent?
  • Is anyone else pushing you to solve it: a customer, a partner, an accountant?
  • What would have to happen for this to become the thing you fix this month?
  • Have you looked for a solution in the last three months? Where did you look?
  • Who would have to agree before you changed how you do it?
  • What happened the last time you changed a tool or a process like this?

Stage 5: the commitment

  • Can I come back to you in two weeks with something to look at?
  • Who else should I talk to about this? Could you introduce me?
  • If this existed and worked as you describe, what would you need to see before paying for it?
  • Would you be willing to try an early version with your real data, knowing it is rough?
  • What would make you stop using it in the first month?
  • Is there anything I should have asked and did not?

What counts as a signal

The answer to the whole interview is in the last stage. A concrete next step is a signal: a follow-up on the calendar, an introduction made the same day, a deposit, or their real data in your hands. Time is a signal too, when they give you more of it than you asked for. Everything else, the enthusiasm, the “definitely”, the “let me know when it launches”, is the sound of a polite person ending a conversation. Score each interview on the step taken, not on the words said, and patterns appear at around ten to fifteen interviews.

Running them at scale: the interview after the sign-up

A founder can hold six of these conversations in a good day. Castan is an AI that builds and runs a company with its owner, who owns everything it makes, and one of the things it builds is the company’s website with a waitlist; the moment someone signs up, it offers them a two-minute interview and asks your questions, one at a time, following each answer with one probe for a concrete example, a number or the last time it happened, ten answers at most and never a pitch. Each interview becomes a learnings block with the quotes and a signal, strong, mixed or weak, and every ten completed interviews are synthesised into one page. The questions are yours to set; the thirty above are a starting script. The free plan runs three interviews a month, Founding a hundred.

Questions people ask

What are the three rules of The Mom Test?

Talk about their life instead of your idea; ask about specific past events instead of generics or opinions about the future; talk less and listen more. They come from Rob Fitzpatrick’s book The Mom Test.

How many customer interviews do I need?

Patterns show up at around ten to fifteen. Judge them by the concrete next steps taken, not by how positive people sounded; five interviews that end in a follow-up or an introduction are worth more than fifty compliments.

What questions should I avoid in a customer interview?

Anything hypothetical (“would you use”, “would you pay”), anything that describes your idea before they have described their life, and leading questions that contain the answer you want. Ask about the last time instead.

Can an AI run customer interviews?

Castan asks your questions to every person who signs up on your website, one at a time with one probe each, and turns each interview into a learnings block with a signal; every ten are synthesised into one page. You set the questions.

Sources

Prices and terms at other companies change over time. Every figure on this page carries the day it was read, and the page it was read on is linked above. If one has moved since, write to hello@castan.ai and the page is corrected.

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