This conversation comes up from time to time and it's always the right thing to do to return the money. It's just the ethical thing to do, for one- no one in the position we're in ought to be holding a Walmart Employee responsible for that kind of money. You're putting someone's livelihood at risk for a stupid mistake. It's also the smart thing to do from the perspective of self-interest. One money order isn't worth putting eyes on that Walmart Money Center and the more "breakage" stores see from this kind of thing the more risk our entire hobby finds itself facing.