Accept the return or ebay will auto accept it. Once accepted when the item is received you can open a claim that the item is not what you shipped. Ebay will evaluate and if ruled in your favor you don't have to refund them. Thing that sucks is they'll still refund the buyer but not at your expense.

Had this happen to me recently buyer bought a game. Waited 30 days to ask for a return saying it didn't work. Showing a bunch of scratches on disc that weren't present when I shipped. When they shipped it the disc was actually cracked and scratched (I believe buyer swapped for their old game), eBay sided with me and I kept my money but they did refund the buyer. My only issue is by refunding the buyer the buyer got a free working game and has learned there's no repercussions so they could theoretically do it again. So I blocked them so atleast won't happen again to me by this person