It can be much worse if people have to use computers and of course trust them completely. Just this week I brought five crates of empty beer bottles back, the machine to feed them into didn't work so the cashier had to do it "manually" at the checkout and after a little learning experience and hitting a key 100 times (5*20 bottles) they wanted to give me 85 Euros in return which I refused as it should have been just 24 Euros...