I actually do this and haven't had any real issues. You occasionally get someone who made a mistake or misrepresented something, but it's not too often. What does happen pretty often is having buyers flake. Sometimes you can weed them out by the types of messages they send. If on FB Marketplace, any profile created less than 2 years old, or if their rating is low, or if they send a pre-written message gets automatically ignored by me.

My biggest haul was a piece of 3/4" plate glass 4'x9'. I've never even seen them listed, but I would guess it costs thousands new. I got it for free.

Coincidentally my sketchiest buy was also when buying glass. The guy looked like he was on something and had the stuff on the 3rd floor of some kind of scrap warehouse place. Nothing bad happened and the glass was as described.