Excellent point. When I'm talking with a first-time founder, they'll ask me what I think of their idea. Sometimes I'll say straight out: you shouldn't ask me that question, because if I answer you shouldn't listen to me.

Feedback from people in the target market is hugely valuable, especially if they answer in individual terms. E.g., I will/won't buy because X. But feedback from people not in the target market is rarely useful, especially when it's in theoretical terms. So unless I have some specific expertise, I try to redirect people toward the people they should actually be talking with.