Some 46% of products were cheaper than their Black Friday price on at least one day during the six months afterwards.
Alex Neill, managing director of home products and services at Which?, said: "The results of our investigation will disappoint many who are expecting nothing but bargains this Black Friday". Be sure to check out all the current Black Friday deals from their website.
We used our data to try to determine the best time of year to buy popular products.
It emerged that nearly half (46%) of products on offer were sold for less in the six months following Black Friday (Dec 2017 to May 2018). Stores open on Thanksgiving and other holidays has been a trend in recent years, especially for country-wide chains - and stores with large Black Friday sales going on. It was £50 cheaper on at least 62 occasions after the sales event.
Big Lots Thanksgiving hours: Big Lots is making some big moves this year, opening store from 7 a.m. on Thanksgiving until midnight and reopening at 6 a.m. for Black Friday.
Of course there are certainly deals to be had, and prices are often considerably lower on Black Friday than at other times of year.
Apple's event will start 23 November (Black Friday) and will last until 26 November (Cyber Monday).
Black Friday may not be until, well, Friday, but that doesn't stop all the deals coming out early and brandishing the name of the imported shopping holiday.
The Sony Cybershot HX60B Superzoom compact camera was advertised as £189 (save £10) on Black Friday 2017, but we found it £10 cheaper at least 27 times in June and July 2017.
Which? also found that it was also cheaper by £10 or more at least 43 times in the six months following Black Friday (including 33 days in December and January). This means that when competitors run promotions its prices are lowered to match them. As our research shows, this isn't always the case.
The store will reopen for Black Friday at 7 a.m.
DeWalt is another big brand at Acme Tools, and they show some impressive DeWalt Black Black Friday deals.