The customer is sometimes devious

Sorry, but that's an unforgivable mistake in your position.

In screwing up a job that is getting wiped out by automation, you're letting the robots win!

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That was kind of harsh. Mistakes happen when people are stressed

It is. In some contexts, what may be considered a simple mistake elsewhere is a capital offense. Like gambling in baseball, having a short register in retail is unforgivable.

There's no way to tell which "mistakes" are genuinely accidental.

Wow, that’s a big oops.

Oops, probably shouldn’t work hungry.
You aren’t yourself when you’re hungry.

Sorry but it kind of sounds like ydi.