The ploy, called ping-ponging, sees shoppers paying over the odds for goods.
And when the supermarkets put on special offers many think that they have landed a bargain when in fact they are paying the recommended price.
Only last week Tesco and Sainsbury’s put on a “special offer” cutting the price of a bottle of Hardys Crest Chardonnay Sauvignon Blanc by half – normally priced at around £10.
But while punters believed they were grabbing a bargain they were in fact buying it at its recommended price.
The same bottle of wine only costs £5 in Asda.
Experts say ping-ponging is used to boost profits on “soft brands” – items not typically bought weekly such as cooking sauce, juice, ketchup, coffee, processed veg and snacks.
It works because shoppers don’t know the regular price as they do for brands they buy more often.
Pricing expert Martin Isark said: “Ping-ponging often leaves consumers paying too much or being given the false impression they are making a saving.
“There have been a lot of attempts to regulate multi-buy offers – but they are so lucrative to supermarkets they’ll do all they can to ensure they continue in as profitable a form as possible.
“But it is surely wrong to sell a bottle of wine worth a fiver for, say, £6.50 and it’s wrong to reduce it later to £4.99 to give customers the impression they’ve got a bargain.”
Mr Isark, who runs website www.SupermarketOwnBrandGuide.co.uk, said the fate of off-licence chain Threshers could be a warning to shop chiefs.
He added: “They tried this, built up a lot of negative feeling and went bust.
“Supermarkets should consider how customers feel about this apparent profiteering.”
Government guidelines introduced in 2008 say an offer is genuine only if it is a discount against a price charged throughout the previous 28 days.
But these guidelines are not legally binding.
A spokesman for the Office for Fair Trading (OFT) said: “We can’t comment on specific examples but this is something we are looking into and something we have concerns with.”
A spokesman for Sainsbury’s said: “Our customers enjoy great promotions and would not buy them if they did not think they were competitively priced.”
And Tesco said: “Our price cuts are always genuine.”
