I don't get groceries by mail order, but I generally don't look very carefully at prices at a grocery store - until one time recently that I was charged the wro

I don't get groceries by mail order, but I generally don't look very carefully at prices at a grocery store - until one time recently that I was charged the wrong price for something. I complained, and was refunded like 20 cents at the customer service desk. I kind of did a double take because I could swear they used to have a policy of giving you anything that came up with the wrong price for free. It's not that the money matters, but where's the deterrent for making mistakes? I also saw once where the unit price was obviously wrong (comparing it with a similar product of a different size) and it felt so pointless to complain. Quite likely a random error, but what's preventing them from doing it systematically if there isn't vigorous enforcement? Automation initially provides accuracy, but then it provides the potential to systematically conceal inaccuracy.