I used to work in a photo lab, back in the pre-digital days, and if someone got a second set of prints at the time of developing, it was 99 cents, much, MUCH cheaper than ordering a set of reprints later. Also the 99 cents applied only to the second set; third, fourth, and fifth sets cost about $3.
If we forgot to print the extra set and the customer came back to complain, we'd take their word for it and just do it at the 99 cent price. Mistakes happen and we were happy to fix our mistakes.
So one day I got an order back that said "forgot 2nd set - please print at 99 cents." I thought, that's funny, I did these pictures yesterday and I could have sworn I did do the extra set, but oh well. The next day, the order came back again, again claiming a second set was missed. Again, I recognized the photos, but doubted my memory enough to do it again (also in the interests of not arguing with a customer).
A few days later, I was working again, and heard a co-worker say, "Hey, I already did these yesterday." Same photos. It was the 2nd time my coworker had seen them, also. So we told the manager and I believe the customer was told that the lab now remembered doing these same photos about 4-5 times.
I guess they saw a different clerk at the counter and thought they wouldn't be recognized, but failed to realize that the people in the lab see the photos.