Which? researchers looked at 227 products in last year’s Black Friday fortnight between 20 November and 1 December.

The deals analysed were from eight of the biggest home and tech retailers in the UK and some of the products on offer were the same price or cheaper at different times in the year.

In what it called “one of the worst examples”, Which? found a hairdryer priced at £18.99 in a Boots Black Friday deal, claiming to be reduced from £49.99.

However, the product had never been £49.99 at Boots in the preceding 12 months.

Which? said a spokesperson for Boots told it its researchers had “reviewed a very small number of our Black Friday deals from last year and in all cases, the items were at a lower price whilst on promotion or when price matched against competitors.” The BBC has contacted Boots for a comment.

Which? also highlighted a previous John Lewis Black Friday deal which featured a smartwatch discounted to £294 with a saving of £90. But Which? found at no point in the previous 12 months had it been sold at £384.

Which? said a John Lewis spokesperson told it: “The recent return of our reimagined Never Knowingly Undersold brand promise – which matches prices with 25 leading retailers – gives customers absolute confidence that they are getting fantastic value.”

The BBC has contacted John Lewis for comment.

Harry Rose, editor of Which? Magazine said: “We want retailers to drop the sneaky pricing tactics so consumers are not misled about the deals on offer.”

He advised shoppers to compare prices at multiple retailers and use websites which check the product’s price history.

“That way you’ll know a good deal when you see one,” he said.