How do you walk into a small business and ask them about their problems?

Say I'm trying to figure out a new business idea and I want to focus on small businesses so I want to ask them what their problems are.

I could try cold emailing / calling small business owners in my area but I feel like they just wouldn't respond to me since it would seem like I'm selling something.

So I think going in-person by walking into their shop/restaurant would be a better way. But even if I walk in, then how do I convince the owner to give time to just tell me about their problems?
If I just say something like "Hey, I want to make some useful software for you, do you have time to tell me about your problems right now?", I feel like the most common response would be "Hey I'm too busy right now".

Does anyone have experience doing this in a better way?