Different scenario but still getting money at someone else's expense:
I recently made a purchase at a shop and through a variety of contrived circumstances (their own fault) they have ended up giving me store credit for the entire purchase rather than the token 10% apology they agreed to give me for the inconvenience.
Thus far I haven't gone over the 10% they planned to give me but it's been 2 months and the account balance is still there.
I can't decide what to do - it's a big faceless company who messed me about so in one respect I feel that it's their mistake, tough luck, perhaps they should have been more courteous the first time and I might have felt differently. On the flip-side I think about the individual who must have made a mistake somewhere during the process and assume that at some point (year end perhaps) the mistake will be noticed and he'll be for the high jump and think that I should tell them their error. Even if I do tell them, that individual has still made a mistake and will probably be in just as much trouble knowing the way big companies deal with disciplinaries.
I know what I should do from a moral point of view but the guy who made the mistake was a right jerk on several occasions over a few weeks. In fact, in subsequent dealing with the shop (due to store credit to spend) I've come to the conclusion their training scheme turns them into jerks - I don't think I've had one satisfactory dealing with them and I honestly don't have very high standards for shop staff; these guys are extraordinarily poor and have a reputation for it locally.
Does receiving poor service morally entitle you to capitalize on their mistakes? I'm still undecided at the moment.