Research by the consumer group suggests Amazon is struggling to spot and prevent sellers from using unscrupulous tactics to manipulate their ratings.

Which? has previously uncovered evidence of fake and suspicious review activity on eBay, Facebook and TripAdvisor.

The group’s research found 34% of consumers planned to buy something on Amazon this Black Friday, compared to 16% at John Lewis and 7% at Currys PC World.

In its latest investigation Which? looked at the first page of Amazon listings for some of the most popular Black Friday product categories. These included tablets, smartphones and wearables, as well as headphones and mobile phone accessories.

Researchers uncovered a range of obvious tactics sellers are using to manipulate review ratings. Amazon says it has clear policies that prohibit sellers from engaging in this type of activity, and has mechanisms in place to analyse reviews, but Which? is concerned that its approach is not effective enough.

Which?’s experts found blatant evidence of sellers incentivising shoppers to write positive reviews, using free gifts or vouchers.

Researchers also spotted large numbers of positive product reviews uploaded in a suspiciously short space of time. In one example a pair of Pro-Elec headphones had 1,006 ratings and 4.8 stars despite the listing having only been added less than six months earlier.

Which? also found products with a suspiciously high number of review images. Which? research has shown how unscrupulous sellers often ask for images when they request positive reviews on their products.

One smartwatch by Willful, an Amazon’s Choice product, had 3,800 images posted alongside the 2,544 written reviews – this is more than 60 times the number of reviews with images left on the Apple Watch Series 3.

Which? also found evidence of “review merging” – where sellers merge dormant or unavailable products with new or existing product listings as a way to transfer positive reviews from one to another.

The consumer champion is concerned that some sellers are seeking to manipulate reviews to increase their prominence in Amazon search results.

The Competition and Markets Authority (CMA) has previously estimated that £23bn a year of consumer transactions are influenced by online reviews and many people will be looking to use them as a helpful guide to get a good deal in the sales.

Natalie Hitchins, Which? head of home products and services, said: “Our investigation has uncovered popular Black Friday product categories that are littered with fake and suspicious reviews – suggesting that deals that look too good to be true often are. This leaves shoppers at risk of being misled into buying poor quality and potentially dangerous products online.

“With people more reliant on online shopping than ever before due to the coronavirus crisis, it’s vital that online platforms step up and do more to protect their users from fake reviews, otherwise the regulator must be prepared to swiftly step in with strong action.”