Retailers are easily able to bypass rules on product placement by distributing free samples in exchange for positive reviews on sites like Amazon, it is alleged.
The consumer group Which? said some sellers offered fees, in addition to the products, to a pool of more than 87,000 reviewers in a single Facebook group alone.
Investigators posing as shoppers said they were quickly accepted into “rewards for reviews” groups and were given instructions on how to request free items in return for five-star reviews.
In two cases, the investigators were told by the seller to rewrite their reviews because they were not sufficiently positive.
Which? said the sellers were “ripping off” buyers by encouraging reviews that were not impartial.
Among the items for which reviews were solicited was a pair of wireless Bluetooth headphones, whose seller promised that a “refund will be done after a good five-star review with some photo” was received, and instructed the buyer to wait four to five days after receiving the product, before writing a review.
The investigator posted a three-star review but was refused a refund unless the review was upgraded to five stars.
In the case of a smart watch, the buyer was instructed to post a review “preferably including pictures and videos”. The investigator gave the watch only two stars and was then told to write a better review – with the seller adding that because the product was free it was “the default to give five-star evaluation”.
The seller of a blood pressure monitor, who also promised a refund, could not be contacted after the sale.
Alex Neill, managing director of home products and services at Which? said the reviews “don’t represent an honest and impartial opinion, but instead mislead people into buying products that they might have otherwise avoided.”
Amazon said it did not allow reviews in exchange for compensation, and Facebook said that “facilitating or encouraging the trade of fake user reviews” was not permitted. However, Which? said it found evidence of Facebook groups with tens of thousands of members.
Mr Neill said: “We all like to do research before buying something. Watch out for unscrupulous sellers and use independent review sites to make sure you’re getting the products you want.”