Lots of people saying eBay only sides with the buyer. But they sided with me as the seller.
Sold a GPU. Buyer tried to return it after the 30 day grace period saying it didn't work. I was pleasant with communication and eBay / PayPal refused to take it any further.
However, this doesn't appear to be the norm so always be careful.
Things like taking pictures / video of item serial numbers and the packages etc will help you a lot. I've had a lot of people over the years try to return a broken electronic item that was actually their original which they swapped with their new purchase for me.
Good luck.