I doubt its a scam, probably just a glitch in the system or something like that. Or maybe it could be a scam, just take a screen shot of ur trade history and then one of ur deck or watever and show it to them i guess.
Do you have a save message that saying you have a deal? report him to the admin and send the message of that guy...
"There are 2 basic rules of trading here at UR.
1) Follow through with all card for card trades.
We can and will blacklist anyone who is caught scamming other players. If you make a deal you are fully expected to follow through. Anyone who is scammed can feel free to report said activity to me or another moderator who speaks their native language. We will investigate the situation, and deal with it as appropriate
2) We do not support Credit Trades.
Do not ask openly in the forums for credits for cards (Or for any other reason). If you chose to engage in one of these trades you do so AT YOUR OWN RISK. Staff does not support these trades. We will not be able to refund credits bought for this purpose, nor can we refund money.
Tell the moderators the situation, and let them deal with the cheater.
Save the message bro..the one he sent you..and the one you sent him for the trade..it should be in your inbox and the other should be in your outbox..notify any of the admin or moderator..i.e. StormWind, he could help you with that..it can be properly investigated from there..evidence can be seen in your sales/purchase history..including the other guy's sales/purchase history..it was properly posted by StormWind himself in the community message board regarding "trading rules" that this kind of act will not be tolerated..the guy who scammed you will be blacklisted if proven guilty..