
Quoting
aaron
How hard will they work to track you down? If it isn't a particularly large dollar figure, you didn't have to give any personally identifying information when you returned the items, they have their merchandise, and they didn't pay out on the gift card, there is a good chance that they will apply the law of diminishing returns and conclude that the cost of further investigation exceeds the likely benefit. As with so many other things in life, though, there are no guarantees.
The eBay angle complicates things, as if the police become involved in a possible fraud through eBay their investigation could lead them to the underlying return fraud, and that investigation could lead to charges even if the store itself isn't presently investigating or pursuing that case.