I recently sold a video game in case with its disc on ebay. 3 weeks later (more than enough time for it to arrive and have been extensively used), the buyer is claiming the disc is 'scratched to no end', not working and wants a return. This particular game was tested for at least 20 minutes by myself and as per any used disc had a few scratches but was in very good condition when I posted it.

My listing clearly showed no returns accepted. What should I do?