Just to throw it out there, check if your buyer has a facebook account. Someone on here awhile back had a buyer open an SNAD for a garment they bought. I can't remember what the issue was that they said in the dispute, but it was unwearable. The savvy seller checked Facebook and here's a few photos in all their glory of the buyer wearing the unwearable garment. The seller won the dispute much to the dismay of the scamming buyer.

I would say your buyer is wardrobing. They needed the jacket for an event and now have no further use for it, so wanting a refund. Plenty are doing it these days. Keep their wardrobes stocked for free. Have a new outfit every week and never pay a cent for it. It's a great scam that eBay is encouraging.