Before you build anything
Most new products don't fail because they're badly built. They fail because not enough people wanted them, and you can find that out for the price of a few coffees before you spend months building.
Who to talk to
Five people who have the problem you're solving, and who aren't your mum or your best mate. If you can't find five, that's already telling you something.
What to ask
- Tell me about the last time this came up. What happened?
- What did you do about it?
- What have you tried, and what did it cost you?
- Honestly, out of ten, how much of a pain is it?
Ask about what they've actually done. "Would you use this?" gets a polite yes nearly every time and tells you nothing.
Polite yes, real yes
"Sounds great, let me know when it's ready" is polite. "Can I pay you now?" is real, and so is "can I tell my business partner about this?" The surest sign is money or time: a pre-order, a deposit, someone agreeing to a second meeting.
Set your line before you start
Before the first conversation, write down what would make you keep going and what would make you stop. Something like: if three of the five have already paid to fix this some other way, keep going, and if fewer than two have, stop and rethink. It's very easy to talk yourself into an idea afterwards, so decide first.