Buyers have 30 days to return an item that they consider is not as described under eBay's Money Back Guarantee, and if your buyer has already opened or opens an eBay item not as described return, they'll be required to send it back to you for a full refund of their original payment, and you'll need to provide them with a pre-paid returns label (if you don't provide a label, the buyer can escalate the dispute and get one from eBay, who will re-charge you for it on your next invoice).
You will get a defect against your selling account if you don’t accept the return (or issue a refund if you don't want your item back) and the buyer escalates the dispute to ask eBay to step in, which they can do after 3 days.
On that basis, you'll need to make a judgement call as to whether you want to pay for a return label and have your item back or to just make a refund.
Once you get your item back, if you feel that your buyer has misused eBay’s Money Back Guarantee you can use the Report Buyer link next to the item in your My eBay. This won't affect the outcome of the return case though.
Guidance for responding to a return request can be found on this eBay page:
https://www.ebay.co.uk/help/selling/managing-returns-refunds/handle-return-request-seller?id=4115&st...
