People can be kind about a product without needing it. Rather than asking whether an idea sounds good, learn how they handle the problem today.
Ask about a real moment.
When did the issue last happen? What did they do? What did it cost them in time, money or missed opportunity? What have they already tried? Concrete stories help you understand whether the problem is present in their lives.
Look for commitment.
A signup is a weak signal on its own. A person who sets aside time for a follow-up, shares a relevant workflow, tries a prototype or agrees to a clearly defined pilot gives you more to learn from. Each commitment still needs context; none proves a market by itself.
Let the evidence change the idea.
Discovery is useful when you can change your mind. If the problem is smaller or different from what you assumed, that is a result worth acting on.