Anyone can make a mistake. However, I have a diner rule.

[merrily]

If I have lunch at your diner often and my check is often wrong, my first assumption is that someone at the diner makes a lot of mistakes.

Then, though, I am going to look at the nature of the mistakes. If some are overcharges and some are undercharges, cool.

If they are all overcharges, it's no mistake.