I think most times I've returned anything, I've had to show the original receipt, so it'd be pretty obvious to them if I bought the item at a discounted price.
If they didn't bother to look at the receipt for your laptop... well, that seems like negligence on the part of the staff handling the return.
If they didn't bother to look at the receipt for your laptop... well, that seems like negligence on the part of the staff handling the return.