That's unusual. Usually, if the seller can show that the buyer already used the item, they'll rule in the seller's favor. It sounds like a supervisor did that after the initial reviewer mistakenly ruled against you. Once he took it on vacation, any issue about "pixels" immediately became moot as the basis for a dispute. The buyer has an obligation to inspect and test the item before using it (beyond simple testing); once he takes it on vacation, it's his camera, regardless of any other issues (except for being a counterfeit).
About 8 years ago, I sold the Omega 1998 bracelet that came with my used 1861 Speedy. It was in excellent-but-worn condition and very clean to the naked eye. The buyer was initially very happy with it and specifically said that he'd installed it onto his watch. Then, he started complaining that it was "filthy," first in emails, and then publicly on WUS to pressure me into issuing a partial refund. When I refused, he filed a PayPal dispute seeking a full refund. In response, I simply linked PayPal to the actual thread on WUS where the buyer admitted to using the item by installing it on his watch and also to cleaning it with a toothbrush. PayPal immediately ruled in my favor because by wearing and cleaning it, the buyer had, thereby, taken ownership and lost any right to dispute the transaction. I think all you would have had to do was share the emails where he admitted taking it on vacation and they'd have ruled in your favor in the first place.