More extreme one -- my auto loan provider accidentally double-charged my bank account for the amount of my car loan payoff (it didn't bounce, either). They instructed me to go through my bank to get the second charge refunded as fraudulent (which I was able to do and I was refunded and happy within 4 days), but then on their end they also sent me a refund check for some reason. When I received the check I gave my auto loan provider a call and they told me they were sorry there is nothing they could do and I would have to cash it, so I gladly got the remaining $6k of my car paid off for free by their own human error. I already had the certificate from them showing the car was paid off and the account was fully closed at this point. One year later and it's still fully paid off on my credit report. They gave me free money. The error on their part was their system had no way of handling "what if our charges are reported as fraud and get yanked back". Well, that and sending out a check after the fact.

It makes me wonder at what $ amount they would have begun to care about their error and tried to correct it.