A couple of Tuesdays ago, after a difficult day at work, a thing that happens to me more often than I’d usually care to admit happened once again. At a supermarket self-checkout machine a frozen pizza I tried to swipe wouldn’t register, leaving me irked and full of spite. As a kind of reproach, I prepared to bag the item in any case, but a pang of weary guilt set in. Two choices sprung to mind. Carry on as though nothing untoward had happened, and knowingly steal. Or hail the cashier, who at the time was busy at another till, to fix the machine and right the wrong.

Some scams have names: 'the banana trick', 'the switcheroo', 'sweethearting'

I picked the second option, eventually. Though, to be honest, on another day I might have swayed the other way. Plenty of us do. Need proof? Look online, perhaps at a Reddit thread, and you’ll find anecdotes of petty self-checkout theft delivered with something like a stick-it-to-the-man pride. Expensive grapes are scanned as inexpensive carrots. Prime steaks are swiped as potatoes. The barcodes of pricey objects – wine, beer, spirits, cosmetics – are deliberately obscured by stickers removed from significantly cheaper on-sale items. Some scams have names – “the banana trick” (steaks as potatoes), “the switcheroo” (cheap barcodes for pricey ones), “sweethearting” (when a checkout supervisor only pretends to scan an object before handing it to a loved one, gratis) – though there are so many techniques not all of them do.

Everyone’s at it

For an idea of how close to home the issue really is, try mentioning it to your friends, like I did. Several of mine confessed to pilfering something from a self-checkout machine at some point, though nearly all of those added a caveat: only small stuff. One recently got away with an umbrella. “Must have forgotten to swipe it through,” she said. Another regularly declares chocolate croissants as bread rolls. And more than a few said they bagged items that failed to scan, half-shifting the blame on to a faulty machine. “A couple of times I tried exotic fruits as potatoes,” a friend wrote in a text one morning. “But a checkout lady once caught me with mangoes, very embarrassing, and I didn’t do it much after that.” He ended the message with an Emoji of a face beneath a halo. “Now I’m a saint, although sometimes I’ll take a five-pence bag if I’ve already paid and realise I need extra.” In a WhatsApp message, one friend confessed to regularly placing a single banana on the scales while nabbing an entire bunch, though that wasn’t all. Sometimes he fills the bagging area “so there’s no room left for more shopping and I’m forced to put items on the floor,” which circumvents the “unexpected item” message we all dread. “I really like the game,” he said. “It’s about being crafty, sneaky – and outwitting them.”

When they turned up last decade, self-checkout machines were supposed to represent a new dawn in minimum-fuss shopping, though they’d been around since 1984. The till’s inventor, David R Humble, had introduced the technology at an LA trade convention, describing it at the time as “a revolutionary product” that “will sweep all of retail”. (To hammer home the point, he had an 11-year-old provide a demonstration. “Many marvelled,” the Los Angeles Times reported.) When they reached stores, the machines offered customers unexpected levels of autonomy, and the opportunity to avoid long queues at traditional checkout tills. And though the machines were outwardly advertised as being strictly beneficial for the customer, they offered retailers perks, too, notably the freedom to slash labour costs. The more self-checkout machines a supermarket had, the fewer cashiers it required. There were savings to be made.

But any financial gains now appear to be marginal, at least in part due to unforeseen spikes in self-scanning theft. In a recent study a team at Voucher Codes Pro, a sales coupon website, quizzed 2,532 shoppers about their supermarket habits and found that close to a quarter had committed theft at a self-checkout machine at least once. (A figure from the same report suggested that the total cost of items stolen through self-checkout machines in 2017 came in at more than £3bn, up from £1.6bn in 2014, though the numbers are speculative.) Some steal by accident, the study found, perhaps on account of a scanning error – honest mistakes. But many perpetrators know exactly what they’re doing.

In 2016, criminologists at the University of Leicester published a paper that reported on the impact of recent developments in mobile-scanning technology. The study was led by Adrian Beck, an emeritus professor of criminology, who has spent more than 25 years researching losses in the retail industry. In the report, he’d suggested that retailers who rely on self-scanning technology inadvertently create environments that encourage theft. In the self-checkout aisle, for example, human interaction is often pared back to a minimum, which reduces the perception of risk on the part of a potential perpetrator. “It’s about the degree of opportunity it provides people who wouldn’t normally do something deviant,” explains Beck. “It presents them with opportunities they wouldn’t normally have.”

A couple of times I tried exotic fruits as potatoes, but a checkout lady caught me. Embarrassing

As Beck sees it, the customer who reaches the self-checkout machine and knowingly bags a frozen pizza after it fails to register isn’t a typical thief. “This guy didn’t get out of bed that morning and say, ‘I can’t wait to be a shoplifter today,’” Beck told me. “And he didn’t walk down an aisle and put something in his pocket.” In most cases, perpetrators are otherwise honest. They tend not to employ traditional shoplifting techniques, and are unlikely to steal in circumstances in which an opportunity is not presented to them. Psychologists call this Opportunity Theory – when an offender consciously decides to take advantage of an opportunity for crime that has appeared in his normal routine. But there is other psychology at play, too. Often, perpetrators will construct what they perceive as legitimate excuses for theft. Some feel justified in taking items when the checkout machine they’re using doesn’t operate smoothly (it’s the machine’s fault). Others consider the items they steal as a kind of payment for work they’re completing on the supermarket’s behalf.

Still more reach the self-checkout machine, look around, and see nothing but the inhuman trappings of a faceless corporation. Few would steal from an individual grocer. But from a multinational conglomerate? What difference does it make? “There’s a mountain of good socio-cognitive criminological research that explains this under the heading of Neutralisation Theory,” says Shadd Maruna, a criminology professor at the University of Manchester. I’d asked him to take me through the psychology of self-checkout theft, to help me get to grips with the “why”. “Individuals can neutralise guilt they might otherwise feel when stealing by telling themselves that there are no victims of the crime, no human being is actually being hurt by this, only some mega-corporation that can surely afford the loss of a few quid. In fact, the corporation has saved so much money by laying off all its cashiers that it is almost morally necessary to steal from them.”

Maruna offered a personal example to illustrate the point. “Twice in the past month I have handed back change to a cashier when I was given too much,” he said. “I did this because I was worried that the individual, working for minimum wage, would have the money taken out of their own pocket if the cash till was short at the end of the workday. Had the same thing happened and a machine gave me the wrong change, there’s no question I would have pocketed it.” He finished with a flourish: “Screw them!”

Frictionless shopping

When I asked several supermarkets to comment on this story, they all declined. Later, when I visited a few of my local stores and asked cashiers about their experiences, most seemed initially open to revealing all before loyalty (or self-preservation) led them to pass the request up the chain to their shift managers, who each delivered a variant of the same message: “Ask head office.” Supermarkets, it seems, would prefer not to spill the beans.

Which isn’t unwise. The subject is fraught with uncertainty. Often it is difficult for retailers to discern between malicious actions and honest mistakes – was the customer absent-minded or consciously fraudulent? – and proving intent can be perilous. Charge an honest shopper with theft and lose their business. Let a perpetrator off the hook and suffer a reduction in profit. Beck describes the scenario as “a legal and customer relations minefield”.

Shift managers I asked all said the same thing: 'Ask head office'

Still, supermarkets are persevering with self-checkouts. According to a BBC report, by 2021 there will be 468,000 around the world, up from some 240,000 in 2016. And retailers aren’t stopping there. Amazon is pursuing plans to create stores in which checkouts are eradicated entirely. Computer vision and artificial intelligence will align to keep track of the items in a shopper’s basket, allow them to walk in and out of the store without any human interaction, and later email them a receipt and charge their account. Chinese retailers aren’t far behind.

Soon, supermarkets might be entirely human-free – what they refer to in the industry as “frictionless”.

Where will that leave us? Customer convenience will rise. The conflicts we sometimes face on a shopping run will reduce to faded memories, and long till queues will be vanquished. So, too, will staff. Cashiers will be diverted to different sections of our stores, ostensibly to better help customers mid-shop, until they will disappear altogether, along with human interaction, the one thing that seems to keep us on the straight and narrow.