Never underestimate what poor hiring practices and a lack of training can do. Way back, I worked at a grocery store and my coworker called me over to help him because he couldn't get an item to scan. It was a potato. Not a potato with a barcode sticker, or in a wrapper or anything like that. Just a fresh, raw, skin-on potato, and he was waving it back and forth over the scanner, completely confounded that nothing was happening.