People can definitely sell for FIAT. I haven't done the research about where that money goes and how to withdraw tbh.

https://www.reddit.com/r/UplandMe/comments/pzrqv5/when_and_how_can_users_convert_upx_into_real/
This thread makes it look, like it's possible but pretty complicated.

I definitely agree with you to be cautious. I wouldn't invest any of my money into the game. I'm fine with that little bit of time, though. :)