When it tells me to “wait for assistance” if I put my four oranges on one by one instead of all at once, or if I lift an item off briefly before replacing it because I need to shift things in the bag, I tend to think they feel I am a criminal. But it does have the side effect of not being able to double scan something.

It does have that effect, but that's just an aspect of the default-criminality and UX fail: there's no UNDO.