one time in my last job a woman came up to the register explaining that when she bought stuff a day prior the clerk forgot to scan a pair of socks worth less than €2 and it was only right for her to bring it back to the store and pay for it proper. unfortunately my manager was directly next to me at the time and took over the register to handle this serious issue. the receipt she had brought with her said which register performed the previous transaction that forgot the socks and the manager could find out who was running that till on that day. poor dude had a manager yell at him for a half hour about how much of an incompetent fuck up he was, he left the job immediately after but i couldnt tell you if he quit or was fired

i think about this moment a lot. the customer seemed like a sweet woman with only good intentions and when she paid for the socks she had a look on her face that said "i feel good because i did the right thing". and a guy lost his job because of a pair of socks. if shit like this ever happens to you and a clerk forgets to scan an item just think of it as a small blessing or that you had good luck or something. keep it.