There's some very obvious ways to prevent that. One way is "here's a list of ten candidate features we might prototype this week/month/quarter/release, but you can only pick one". Or ask users to rank them, and only pick the consensus #1-ranked. The ensuing dialog can be informative.

Have you never say "no, I don't care about it" when asked such a question? I say that a lot of times, and get that from users all the time too.

The thing is, you can't confuse a "yes" with the user actually wanting it. But there are plenty of ideas that everybody clearly do not want, and people will answer you a "no" if you ask.

Depends how you ask. If you ask people whether they would pay extra $ for a feature, they might be more hesitant.