Of course it is infuriating to be called the very thing you despise, and I am very sorry this happened to you. They attacked your honor and it upset you, understandably. But for some buyers, this is a game. You have to learn to play it better than they do.
This sounds like your first bad experience with a case opened against you. So the odds have been in your favor for a long time. In the decade since i've been selling here, I have never had a bad buyer. My point is these dishonest people are in the minority. Still, every seller dealing in fine metals or other expensive items needs to evaluate their risk in selling such and make allowances for shrinkage, just like with a brick and mortar. Fraud is a part of the landscape and must be planned for.
Anyone can tell by your listings and feedback that you are a stellar seller. But from eBay's point of view, it is impossible to prove what was sent to a buyer. Even with pictures showing the proper marks on jewelry does not prove that was what was sent , nor does the mark ensure the item is genuine as marks are faked, too. (This happened to me. I was defrauded by a seller selling fake sterling silver, and it was all marked properly. The fraudsters have this down to a science.) So eBay is going to side with the buyer regardless of the circumstances. It is well known that eBay looks out for the buyer's interest, first and foremost. Sellers must protect themselves.
When it comes to a Not As Described case, it doesn't matter what the buyer says, 95% of the time they will get a refund regardless of the evidence. When that happens, it is in your better interests to not fight the return. The penalties that eBay levels against a seller who denies a SNAD return can be substantial, including a defect on your account and having to pay the Final Value fees on the item in question. So if this ever happens again, cut your losses and refund, knowing the time to fight is after the case is closed.
All is not lost. You have 30 days to appeal eBay's ruling. That is where the ship can be righted. If the appeal is carefully prepared, you may have a shot at reversing the decision. Depending on what the buyer did, you may want to bring charges against them with the authorities, including the Postal Inspectors. If you do this, make sure you get case numbers. Also make a report to the Internet Crimes Complaint Center at ic3.gov. Include all the case numbers in the appeal to show you are earnest in your position. Below is a link to the appeals policy with more details. Good luck in your efforts.
https://www.ebay.com/help/selling/managing-returns-refunds/appeal-ebays-decision-return-missing-item...
