I bought a used GoPro off eBay many years ago. The seller had a good rating, and I figured that would work out. I got the GoPro, it wouldn't turn on and wouldn't charge. The battery connections on the battery AND in the camera were corroded. I notified the seller via email and received no response. I took it to a local camera shop to see if it was salvageable, sadly no. Due to my own procrastination, I passed the 30 days to get refunded but filed a complaint anyway. Seller finally responded and said they would refund me if I shipped it back. I did (glad to be rid of it) but SHOCK, no money came back. Seller ghosted me.
Some of it was my own fault, but even the rating system is not perfect. I've bought stuff from sellers in Asia and gotten very fast, reliable service. IMO, eBay is a complete crap-shoot.