Stores including Tesco, Sainsburys and Asda are offering 'zig-zag' pricing, meaning that so-called half-price wine is often in reality more expensive than it was a few months earlier, price comparison site Mysupermarket has found.
The research, carried out for The Guardian, highlights the cost of Tesco's Ogio Pinot Grigio - one of the supermarket's best-selling wines. It's currently on sale at £5.49 - claimed as "half price".
However, according to Mysupermarket, the wine was priced at £10.99 for only 63 days during the last year. For 58 days, it cost just £4.99 - making the "half-price" claim look pretty thin. The research found similar examples from Sainsbury's and Asda.
And this makes more of a difference than consumers might think to the quality of the wine they're getting for their money, as only a small proportion of the cost of a bottle actually goes on the wine itself. For a £5 bottle, at least £2 is taken up by excise duty. Another pound or so goes on VAT. Then, there's the cost of transport, storage and packaging - about 60p - and the supermarket's cut of about £1.25.
Commenting on the survey results, shadow consumer affairs minister Stella Creasey said that supermarkets should do more to let consumers know the real cost of their wine.
"We want supermarkets to compete to be the best at quality and value, not confusion and sleight of hand when it comes to marking up prices," she said.
"Just as we've seen in other markets, such as those around the sale of furniture, there are lessons to be learned about how to ensure consumers have more information about just how good a bargain they are really getting before they fill their trolleys, so that they don't end up paying over the odds."
And there's another trick to look out for, says Warren Edwardes, President of the Association of Small Direct Wine Merchants (ASDW) and CEO of Hyde Park wines.
"The latest cunning trick requires a magnifying glass to spot. Reading the price label very carefully you can spot 'Crossed out prices charged at most stores in GB'," he says. "That would be in the expensive 'Express' or 'Local' convenience branch" would it?"