I highly recommend the book "The Mom Test" for tips on how to speak to customers and what kind of information you can get.
Just a few of the things I learnt from that book:
Don't ask if people would use your product. It's too hypothetical and people are too nice. "Sure, I'd probably use it. Looks useful. Keep working on it!". Then you never hear from them again. If you really think they'd be interested, ask for money.
Don't ask about people's problems in an abstract way. "Tell me about your business problems" is just too vague and wishy-washy. Ask about more specific things. Example: "You're having issues with double booking? Tell me about the last time it happened." Asking about the most recent time something happened is a great way to get concrete details.
Ask people how they have solved the problems or tried to solve the problem they talk about. "It was a major issue so we hired an extra member of staff to confirm all the stock lists". (Great, they're willing to spend real money on fixing this). "I searched around and tried out ABCSoft and XYZSoft but they were designed for a different kind of business and didn't really solve it for us" (pretty good, they're putting effort into finding solutions). "Oh, well, it's always been a big issue but we haven't tried to solve it yet" (Uh-oh, it's probably not really a big problem for them. It's not painful enough for them to try to solve).