I’ve had significant issues with some particular models of self-checkout. They have some sort of weight check after scanning an item, to see if I’ve placed it in the basket. I assume they’re matching up the items known weight, with the change in the weight in my bag.

However, it’s implemented poorly, with frequent false positives. Furthermore, there’s a race condition between scanning the item, the machine saying “place it in the bag”, and the actual weight check. If I move too fast, the item is in my bag before the check starts, and I have to wait for assistance.

Maybe folks are frustrated that their theft is being caught, but high frustration seems to be the base case here.