What do you ask your customers?

Dont sell them or talk about your product first. Talk about how they currently or recently used your product or a substitute. What goals they want to achieve. What they like most/least and why. Check out the 'mom test' book for some good tips

Some of them will do this more easily than others but let them tell their own story first and have them end with by speaking about their most important objectives at this time, and then thank them for sharing.

If there was one thing you could fix with "insert subject of choice" right now, what would it be?

Ask them to refer new customers if they were satisfied with your product/service.

It really depends on what you do but here is a one liner that normally gets a hard "No" followed by some of that feedback you are after: Are we falling short anywhere? Normally it goes: You: Are we falling short anywhere? Them: No, you guys are great. But I do wish the blah blah blah did more blah. Or You: Are we falling short anywhere? Them: No. You: Really? We are very open to feedback and if you have anything that might help us we definitely want to know. Them: Come to think of it you guys do suck at blah blah blah.

You could start by asking them 'Why did they use your product in the first place?' I have come across a lot of instances where the team developed the product for a specific use case but customers are using it for something entirely different. So, this question helps you to get new insights on your GTM strategy. The second good question will be 'What were you using to fulfill your same need prior to our product?' This would help you understand the a good product market fit, this also helps in understanding your direct (those who have similar product) & replacement (potential products customers might use to substitute your product/service) competitors.

What they think about our products and services.