Sold a rif once and the guy disassembled it, broke the gearbox, then claimed it arrived broken. Silly bugger had already sent a message confirming it worked on arrival though, but that was still three weeks in PayPal dispute. I think that's the only one that really ground my gears.
Other than that there's some funny buggers out there. Shout out to Job Lot posters, always a Perfect Starter Kit. A pile of minging gear, no splits though you're getting that one pistol you might want bundled in with a load of Amazon special, child size, full Multicam Black kit. The worst photos of the worst piles of junk going.
Collection only btw.