Never ask a customer if your idea is good
Rob Fitzpatrick's rule for talking to customers is named after the person least qualified to give you an honest answer.
Ask your mother whether your business idea is good, and she will say yes — not because she's dishonest, but because she loves you and the question puts her in an impossible spot. Rob Fitzpatrick's insight in The Mom Test is that this isn't a mom problem. It's everyone. Ask anyone whether your idea is good and you invite a compliment, because you've exposed your ego and made agreeing with you the polite move.
His fix is a single discipline: never mention your idea. Ask instead about their life. Not "would you use an app that tracks X," but "walk me through the last time X actually went wrong for you, and what you did about it." A person can't lie about what they already did. They can absolutely lie about what they'd hypothetically do.
Fitzpatrick calls opinions and hypotheticals bad data — fool's gold, shiny and worthless. The founders who build things nobody wants usually collected plenty of feedback. They just never once asked a question their mother couldn't have answered kindly and wrongly.