I personally will never sell an item on eBay again. The buyer protection is setup to benefit the buyer no matter what. Very little seller protections.
About 2 years ago I sold a MacBook Air on eBay that was in phenomenal shape, including original retail packaging. Buyer opened a claim that stated item wasn't as described. They said the device had a big scratch on the display (liars) and claimed the original retail packaging wasn't included. This was 28 days into the 30 day buyer money back guarantee. I provided eBay with photographic proof, the whole nine yards. They still sided with the buyer...even given the amount of time that elapsed. I was peeved. Somehow eBay or myself screwed up the return process and a refund was issued. The buyer refused to ship the computer back and I ended up having to settle with no computer and 40% reduced off the cost of the computer. The whole thing was very ridiculous and infuriating.
If you do sell on eBay, my extreme recommendation is to capture time stamped uncut video of the device/condition, sealing the device in it's shipping package, you driving to the carrier, surrendering the package and receiving the receipt. May never need it, but why risk it?
A belated "very believable." Not only have we read comments from former eBay sellers with almost identical issues (different and various products) but we had the same issue with a new, sealed MS OS that we sold. However, we took photos, with time stamp, had two witnesses observe us packing the shipping carton (VERY well packed) and even accompanied us to FedEx. With less than 10 days remaining in the eGay return time frame, the buyer submitted a return.
No matter what we submitted to eGay, we were nonetheless coerced ("either you process the return seller or else deal with the wrath of eGay, seller!), processing the return. Had we not done so, eGay would've reversed the payment, back to the seller, and the seller would've been entitled to keeping the Operating System according to what an eBay representative told us. The buyer claimed the OS Disc had scratches on it. When we received the OS, opened by the buyer, there were NO scratches. Obviously it was another unethical, unscrupulous cheapie eGay shopper with buyer's remorse, discovering that he could get the OS elsewhere for "10 cents" less.
Once more, your story is entirely believable. Once more, after the aforementioned experience (and financial LOSS!) we read numerous believable stories identical to these unethical buyer return issues. Advice from former "professional" ebay sellers...AVOID selling expensive products or technology items on eGay.