Asda's Price Guarantee has backfired, after a glitch in the system meant it started doing incorrect price comparisons and refunding a small fortune. Some customers claim to have made thousands of pounds.
So what happened, and can you cash in?
The glitchThe problem arose with the Asda Price Guarantee. The idea is that shortly after your shop you can enter the details from your receipt into the supermarket's website and it will compare the price of your shopping with a number of other supermarkets.
If it is cheaper elsewhere you receive the difference, plus a bonus of 10% - up to the value of £40 on every visit to the supermarket.
The problem for Asda was that the system started dramatically underestimating how much certain items cost elsewhere.
The glitch was demonstrated by The Grocer magazine, which ran a trial basket. The system should have calculated the cost at Asda at £15.30 and the cost at Waitrose at £30.87. However, it calculated the Waitrose cost at £8.57 - triggering a voucher for £17.59.
ExploitingUsers of the Moneysavingexpert website started sharing details of the products that were being underestimated (oddly this tended to mean buying one of a number of 'trigger products' alongside items that were on 3-for-2 offer elsewhere), so that shoppers could add them to their basket and increase their chances of earning a voucher.
And although the amount of money each shopper could claim was limited to £100 a month, people were getting around it by using different computers and email addresses. One claimed to have made more than £8,000 in four weeks.
An Asda spokesperson told AOL: "A small glitch in the Asda Price Guarantee has meant that a very small number of our savviest customers have been able to beat the system and claim a few, larger than normal, money-off vouchers."
Can you cash in?Before you hotfoot it down to Asda it's worth mentioning that the supermarket has cottoned on to the problem. The spokesperson said: "Saving customers money is in our DNA, but unfortunately this is a gift that can't keep on giving, and we have taken the decision to put a cap on the value of the voucher that can be generated in one transaction. This cap is set at £15 and was in place on Sunday."
It's worth pointing out that this cap will only affect a tiny minority of customers, and aside from those trying to exploit the glitch, only about 0.24% of customers generate vouchers for more than this sum, so the vast majority of people won't be affected.
Not the firstThis isn't the first time a price matching deal has gone awry. Perhaps most famously, in April last year, Tesco was forced to ditch its promise to refund 'double the difference' if customers found deals cheaper elsewhere.
After shoppers started sharing details of products that could trigger a refund, it capped refunds at £20, and then changed its deal to only refund the difference. A spokesperson blamed customers, saying: "Price Check has given our customers confidence in our prices and transparency. But some people have misused the scheme to cash in. So we have taken this step to protect Price Check for the majority of our customers."
Those pesky customers eh?
The difference for Asda is that in many cases it remained the cheapest despite the glitch. The change to the rule is to stop customers exploiting a technological glitch rather than a reaction to the fact that any other supermarket is cheaper.
The Price Guarantee remains in operation, and you can still get the difference refunded plus 10% if the products are cheaper elsewhere. So while you can't exploit the glitch, there's still a good argument that you can take advantage.