Sorry this happened to you.
There are seller protections here, but you have to know what they are and how to use them. It is also important to understand how eBay works, and what happens when a claim is opened by a buyer. It doesn't sound like you had a handle on it.
Video evidence is not accepted or useful to eBay. Filming the working item says one thing—it worked once. It does not prove the buyer received a working unit. Things happen in transit. There is no burden on the buyer to have to prove anything. Ebay will side with the buyer in a dispute.
Since you were unaware of this, you essentially entered into this transaction blind to the risk factors that sellers face, especially when listing expensive goods on eBay. There is substantial risk in online selling. Unfortunately you didn't have the information necessary to successfully conduct business on the platform.
Most buyers are honest. In over ten years of selling, i have never encountered one. So i give the buyer the benefit of the doubt if an issue arises. I don’t sweat returns, and grant them for any reason. (But i rarely get one.) I am cautious but not fearful, knowing the risks.
Just calling Ebay is not going to help you unless you file an official appeal within 30 days of their decision. Did you do this? It sounds too late for you to do it now.
Below is the link on how to do appeal for those reading this who might need it. Don’t let eBay open it before you have ready evidence. They will automatically find for the buyer if you don’t have proof of buyer wrongdoing. Upload the proof in the case notes and make the case to eBay factually, without emotion.
OP, if you intend to keep selling here, read the eBay User Agreement carefully, along with eBay’s Money Back Guarantee policy. Read the forum posts too. Learn what you need to know to successfully navigate selling online. Good luck, and hope you are able to get your money back.
https://www.ebay.com/help/selling/managing-returns-refunds/appeal-ebays-decision-return-missing-item...
