Payoff

I came across the concept of payoff... I never tought about it!
For example in a English (ascending-bid) auction the bidders who lose the auction have a payoff of 0. This makes sense, since they don't earn and don't pay anything.
What I never thought about is that the bidder who wins the auction has a payoff which is not equal to the amount he pays, but to the difference between how much he values the item and how much he pays for it!
Let's make an example: I always buy a beauty cream on eBay, which costs 19,99€ in the normal shops. If I can get that cream on eBay for 15€ (+1,85€ shipment), my payoff will be 3,34€.
The 3,34€ are the difference between my estimated value of the item and the money I pay for it on eBay. The question is: does it make sense to but the cream on eBay, take the risk of being cheated by the unknown seller or by the postal service which may lose the packet to save only 3,34€?
Well, for me yes, consider it is more than 15% discount on the shop price!
Perhaps the real question is if I really need the cream... but women can do almost anything for their beauty ;)