I'm sure that happens, though I would be surprised if it happens frequently in the groups I'm in. The volume of sales is low, and the items are niche enough that they often aren't in direct competition.

this absolutely happens, during the peak of the GPU crisis, salty gamers would report Craigslist/FBM listings for GPUs because they didn't like that they were being listed for over MSRP. Eventually they get taken down (even from an account in prior good standing) and you will probably get some kind of ban at some point.

I think it kinda let off over time as people resigned themselves that it was a real thing and was gonna be a while, but yeah, there's no real protection against abuse there.