how to win an appealed case on ebay?

[bstuek]

Long story short, a buyer opened a case against me on ebay. I thought my argument was pretty damn clear and right, but eBay took the seller's side, so now he's sending the item back to me (Which he changed--- he took the item out of its case)... I want to appeal, but how can I win? would it be best to call eBay on the phone and talk to someone? does the fact that he removed it from its plastic matter? thanks
My mistake--- I am the seller.... eBay took the BUYER'S side.
I know that he took the item out of its plastic, because he was attempting to resell it at double the price I sold it to him at... and in the listing, it was out of its plastic.