A glitch is preventing me from viewing your current listings or feedback, so I will just have to assume that you're a private seller and don't offer returns.
If so, and they have only opened a return request, you're entitled to refuse it.
However, if they have opened a money back guarantee case all you can do is accept the case and send them a prepaid return label. eBay will then issue a refund on proof of return. You can theoretically appeal appeal after the case has closed, but it's likely to prove pointless. eBay never sees the items and generally takes the buyer's word for faults. You can report them for abuse of the buyer protection system, and if enough other seller do the same they might be restricted from amking further claims. Might. The guarantee is very heavily weighted in the buyer's favour.
