Buyer swapped out parts

Question

So I have a return im processing from a computer store for a gpu that I verified was working before I sent. They said the unit is defective and crashes their system. I have suspicion that they swapped out parts due to the working status when it was sent and the fact that I called and asked and they said they do fix circuit boards and vram and such. Also their website states that as well. What's the best way to handle this?

butter_buy · Answer

So ebay ruled in my favor, the buyer swapped out stickers and didn't place them correctly and had the serial number backwards from the correct factory placement and bent thw mount. Seems like what I had assumed they had done was spot on.