It does happen. All you can do is accept the return, provide a label and get the item back.
My last case was a buyer complaining that some earrings I sold her were 'not vintage'. I bought them in the 1980s, secondhand and Ebay have 1980-1989 as an era in their antique and vintage jewellery category. To support her claim, the buyer added a photo of some scruffy, rusty, old earrings. The ones I sold were in lovely condition.
Anyway, I accepted the return.
I would advise you to block the buyer as soon as you get your item back and you can also report them for mis-using the Ebay Money back Guarantee. I reported my buyer - the first time I have done this in 20 years - because the claim was so blatantly fake and I was annoyed.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)