Suppose I know that [item] is just what you want for the GAuGE (Great American Gift Exchange*), and I get [item] for you. But I used my mad shopping skillz to get [item] at a severe discount. Does this mean I should get you another something to make up for spending less on you, or I should just give you the original item, knowing it's perfect for you, and that's enough? Does it matter if you, the recipient, find out how much I paid?
* time to evaluate all sorts of things....
* time to evaluate all sorts of things....