I got hit the other month on ebay. Sent a whole load of parcels out and accidentally got two of them mixed up. One buyer accepted by apologies and sent it on to the other buyer. The other buyer complained I was scamming him and didn't like that I wouldn't give him my email and that I kept every correspondence on ebay. I asked him to send the parcel on but he went quiet until he got his parcel from the other buyer then escalated his claim to goods not received. First I knew was that ebay had reimbursed him from my paypal account so I lost both parcels and had to reimburse the other buyer as well.
As I had gone entirely through ebay messages I contacted ebay and got the negative feedback removed, although I am supposed to negotiate the return of the other parcel with the buyer - as if that's going to happen.
10 years ago ebay was great, it was a giant car boot sale and the internet was quiet enough that all the numpties you find these days hadn't worked it out, so ebay users were generally trustworthy and new items on ebay were pretty rare. You could spend hours each day going through the r/c car section on its own. Ebay wanted more profits so put their fees up, which chased some sellers away. The cycle continued until ebay changed tactic and decided it no longer wanted to be the worlds biggest fleamarket and is now trying to be an Amazon selling new products at a fixed price and ebays rules are now set up entirely in favour of the buyer, lots of buyers attracts lots of business sellers. Big business can absorb a few hits from the blatant scammers, claiming an item wasn't received gives you an instant refund unless the buyer has proof it was delivered.
Not worth the hassle and cost these days, got plenty of stuff I would have put on there without thinking about it years ago but really don't bother unless I need the money quickly, and even that isn't guaranteed these days.
The problem is there isn't a real alternative for us all to go over to.