IIRC eBay buyers can have up to 3 months to report a problem and there was talk of them extending it to six, something to do with EEC rules on distance selling.
I had one were I sold a Farish Deltic DCC fitted, the buyer left positive feedback, do I left him positive feedback. A month later he started a return saying it's derailing, which I accepted, only when I got it back the buyer had removed the decoder and kept it.
EBay did nothing and refunded him in full.
There are those who know how the system works and when to work it