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.

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.