People always find a way of giving themselves a rebate at the self-checkout. When I lived in the UK in the '80s some supermarkets let you bag, weigh, and print out the label for fruit, veg, and bulk nuts, grains, etc. People would put a few items in the bag, weigh the bag, print out the label at the scale, and then proceed to add more items. The cashiers could not double-check the weight at the register.