My Ethics Reward: $300!

About 25 years ago I withdrew $100 from my local NYC Citibank ATM. The machine made the usual noises, but neither spit out the cash nor produced a receipt. When I returned home I called them immediately, fearing the withdrawal would appear on my next statement, despite my having not received the cash.
Sure enough when the statement arrived, they had credited me with the $100. However, the withdrawal wasn't there, so I was up $100. I called them to explain their error; they apologized and assured me that in the next statement all would be corrected. Another month passed, and the new statement dutifully credited me with yet another $100.
Again, no withdrawal. 

Their system either could not handle someone calling with my particular request, or the employee just couldn't conceive of it. I called one more time, explaining that they had credited me the $100 twice, but it really wasn't supposed to be there at all. (That probably was excessive - but it was getting into it by then.) Unbelievably, the third statement added yet another $100. I decided to quit with the $300 in my account. It was time-consuming to keep calling them.
Back in those days I actually balanced my checkbook, but I never added in that $300 - though I liked knowing it was there.
When we moved, I closed the account, and sure enough, the magic $300 was in the balance. The story itself was great fun to tell, and I made sure my kids heard it - because the message of course is that if the bank or anyone else errs in your favor you are just as obliged to point it out as you would if you were trying to rectify errors made against your account.
Of course one should do the right thing in any event, but here was the rare case when ethical behavior was rewarded - though in this case, just through the bank's ineptitude!