Okay guys what do I do...
Went to target earlier to buy the game. Found one copy left on the shelves with the little alarm thing on it and both tape seals intact, top and bottom. Trying to activate it now and it tells me that the key has already been claimed...yes I checked for typos.
Upon closer inspection it looks like the bottom taping was slightly tampered with. It wasn't cut but it looks like they might have carefully peeled it off...so someone may have bought it, used it, and returned it.
I already cut the top part of the tape.
so uhhhhh now what..
If your Target won't take it back then you can contact blizzard. I remember hearing similar stories to this and basically if you can get a picture of the receipt with your code I think you get ownership over it and the other guys loses it from his account.