At some stores, the clerks can enter the amount at the register. I doubt the clerks would just have their buddy waiting conveniently to hold the $ though. They probably signal the person and their buddy gets in their line then.
I check my receipts to make sure nothing was rang too many times. That's an easy mistake and I don't have the $ to pay for stuff I don't get.
I've heard swiping the card at gas pumps can make it easier for scammers. They say to just pay inside to get around it.
in some country and store, you can't just trust cashier. safer is using cash money than credit card if you're only buying cheap stuff. use credit card only in trusted place.