The point is, though, that now petsmart has just "purchased" that same item for $52 dollars instead of, say, $25. If they sell it(which they do/will) for $52, they make no money. Even if the guy does spend the money at petsmart, he is now using that stolen money to purchase fish. In the end, petsmart still has $11 stolen from them, whether it's in the form of cash as a return, or fish it's still a quantifiable amount.
I do believe kharma will be on the side of the intent. If it was a gift, and the person did not have a reciept or clue as to where it came from, that's a different story and petsmart is doing a nice thing by letting them return the item there. This guy is intending to steal. He's aware of it, he's going to a lot of effort to accomplish it. I'm not concerned because it will come back to him.
In college I was a server. One day at Cracker Barrell I forgot to tip the guy. The tip would have only been $6, but I forgot(I think their system of paying at the front contributes to this problem). I got home, realized I forgot, and immediately I knew it would come back to me. Sure enough, that night as I was waiting tables, I was stiffed on the tip on a $200 check. At first I was mad, then I knew it was kharma coming back at me.
I always remember to tip at Cracker Barrell now.