A few years ago rented and returned a vehicle to National here in NYC. The return was after hours to the garage so only got the hiker/receipt. Fair enough, no worries as had been there and done that often.

Got busy with work and life so didn't check for the email confirming the return and final receipt. Several days later when got around to it nothing.... Called the location to see what was going on; not only wasn't the reservation totally closed out but the vehicle had been given to someone else the day after I returned, and was still being driven.