Well, here's a bargain: a £1 bag of marshmallows at the cut-throat price of just... £1.
Shoppers at Sainsbury's Sale branch were left scratching their heads earlier this week after spotting the 'cut-price' 180g bag of pink and white mini marshmallows on sale.
Shopper Alex Kilpatrick spotted the sign, which shows the original price crossed out and replaced with the 'lower' one and posted a photo on Facebook, where it's been widely shared.
And Sainsbury's responded, tweeting: "Oh dear, that looks a bit off! What store was this in & when was it noticed? I'll get this fed back."
In this case, the misleading sign was clearly a mistake - and that's something that happens all the time. Twitter is full of pictures of similarly daft deals, from the 99p marrow in Morrisons - or two for £3 - to the Sainsbury's champagne where two bottles actually cost less than one.
Sometimes, these mistakes work to the customer's benefit, as when Tesco mistakenly charged just 1p for mints that should have cost £1.25. And, in 2012, a glitch with special offers meant customers were able to buy £9.99 bottles of wine for just £1.50.
However, as supermarkets increasingly compete on price, some are resorting to dodgy tactics.
Last summer, an investigation by Which? revealed that Tesco, Asda and Sainsbury's were misleading shoppers over discounts and promotions.
Asda, for example, increased the price of a Chicago Town Four Cheese Pizza Two-Pack from £1.50 to £2 as it launched an offer to buy two for £3. When this 'offer' ended, the price went back down to £1.50.
"We want special offers to be special and are campaigning for simpler, clearer and fairer pricing rules and tougher enforcement action," said head of campaigns Alex Neill.
Two years ago, Tesco was fined for offering 'half-price' strawberries that were nothing of the sort. The company had simply hiked the price to £3.99 for a week before halving the price for months.
And last summer, Aldi was ordered to withdraw ads that claimed customers could 'swap and save'.
Even more drastically, cut-price store Poundland was recently ordered to change all its signage after a court ruled that its 'everything £1' claim was false.