A survey of deals on offer for last year's Black Friday has found more than half were the same price or cheaper months either side of the event, according to a consumer group.
Which? tracked the Black Friday prices of 35 of the most popular technology, home and personal care products sold by Currys PC World, Argos and Amazon to find that 60% of the deals could have been found at other times during the year, or for a cheaper price.
A Neff Slide and Hide Oven on offer at Currys for £494.99 for Black Friday was cheaper for at least 113 other days of the year and £45 less expensive just three weeks later, the watchdog found.
A Samsung 55-inch Smart 4K Ultra HD curved TV advertised by Currys as 'Save £400, now £849' was £50 cheaper at least 29 times in December, January and April, the same price at least seven times in April and £79 cheaper at least 18 times in May.
Currys also offered the DeLonghi bean-to-cup coffee machine for £349 for the sales event, a significant saving on the £729.99 regular price stated by the retailer for most of September and October, but Which? found it sold for £579.99 for nearly three weeks during this time and remained at the Black Friday price for almost all of December.
An Oral B electric toothbrush from Amazon was advertised as 'save 26%: was £40.49, now £29.99' but was £5 cheaper on at least two days in July.
At Argos, a 49-inch LG TV advertised for £499 with the tagline 'Our lowest price' was £4 cheaper a week later and another £16 cheaper at the end of December.
UK shoppers are expected to spend £2.6 billion - an 8% increase on the £2.4 billion spent last year - or £1.8 million per minute snapping up deals online and in stores on November 24, according to predictions by VoucherCodes and the Centre for Retail Research (CRR).
Which? has urged consumers to research reviews and regular prices ahead of Black Friday to know if they are getting a good deal or not, and to shop at retailers with price promises to increase the chance of a part-refund if an item drops in value in the weeks following the purchase.
Alex Neill, Which? managing director of home products and services, said: "Our research shows that although Black Friday can offer some great discounts, not all offers are as good as they seem.
"It's easy to get swept along by the hype and excitement on the day, so we recommend doing some preparation and research to help make sure you really are getting a good deal when shopping in the sales."
Currys said: "The Black Friday sales period has become an established part of our promotional calendar alongside January Sale and Bank Holiday weekend offers.
"Last year, Currys PC World alone featured around 4,000 products reduced as part of our Black Friday campaign with many items being their lowest ever price at that point in time.
"The fact that some of these were then reduced further in the months after that period is simply us continuing to offer our customers great value throughout the year."
An Argos spokesman said: "Black Friday is a fantastic event which allows customers to choose from thousands of products which offer great value.
"This does not exclude these products from other sales or promotional activity at other times of the year."
Amazon said: "We offer many thousands of incredible deals around Black Friday representing millions of pounds of savings for our customers across a vast selection of products."