How common are self-scanning scams? If anonymous online questionnaires are any indication, very common. When Voucher Codes Pro, a company that offers coupons to internet shoppers, surveyed 2,634 people, nearly 20 percent admitted to having stolen at the self-checkout in the past. More than half of those people said they gamed the system because detection by store security was unlikely. A 2015 study of self-checkouts with handheld scanners, conducted by criminologists at the University of Leicester, also found evidence of widespread theft. After auditing 1 million self-checkout transactions over the course of a year, totaling $21 million in sales, they found that nearly $850,000 worth of goods left the store without being scanned and paid for.

The Leicester researchers concluded that the ease of theft is likely inspiring people who might not otherwise steal to do so. Rather than walk into a store intending to take something, a shopper might, at the end of a trip, decide that a discount is in order. As one retail employee told the researchers, “People who traditionally don’t intend to steal [might realize that] … when I buy 20, I can get five for free.” The authors further proposed that retailers bore some blame for the problem. In their zeal to cut labor costs, the study said, supermarkets could be seen as having created “a crime-generating environment” that promotes profit “above social responsibility.”

While I think the scanners have gotten better, I know a few times I've gotten home and noticed things made it past the scanner and not on the receipt. Not usually intentionally, just the usual didn't ring up correctly. That said, it does seem like recently the self-checkout lines have gotten a bit more accurate.