This makes my blood boil.
There is no doubt that this dealer would've honored this transaction had it sold it for the premium they desired. I would definitely take legal action merely on principle! You have a strong case. When you won the auction, you entered into a contract allbeit digital but just as binding as signing a paper contract. Also, make sure you take screenshots of the listing and the seller's feedback score while it's still there! Start making a file.
What a bunch of sleezeballs! They fucked up, they should take the $10,000+ hit and follow through. You learn from your mistakes. Honor the transaction and move on. This should be easier for a "multi-billion" dollar company
Keep us updated!
I'm going to go stick my head in the freezer now.