"There's no such thing as mixed signals. If you're not sure, they're not interested." Do you agree with this statement?

Disagree.

There IS such a thing as mixed signals. There is also the chance that someone is perceiving signals as mixed or convincing themselves of it, to avoid accepting there is no interest.

Some people are just very subtle or unsure about showing interest, or it may take a while before they actually know they're interested (before something 'clicks' inside them).

I'd tend to move on from someone I thought was sending 'mixed signals' though. If they do decide they're interested at some point, they can reach out to me and make that clear. I won't just wait around and see which way the needle ends up pointing (because there's a fair chance they aren't really interested).

EDIT: If you like someone and you can't tell if they like you back, then just ask. Better to cut to the chase and find out for sure, so you can explore things together or move on alone (no more wondering).

no

Nonsense. There have been times when women have given me totally unambiguous signals that they were interested in me, and I still wasn't sure. If you aren't interested in a guy, and he isn't picking up on your hints, then you should stop with the hints, and talk to him directly. Like a grownup.