So-called incentivised reviews, where people are given products in return for write-ups on Amazon, are skewing results, artificially increasing the star ratings, according to a report.



Such reviews must have a disclaimer typically saying: “I received this product for free or at a discount in exchange for my honest, unbiased review” or something similar, according to Amazon’s guidelines.

But while prospective buyers, on seeing the disclaimer, may choose to discount or question the reliability of the review, the incentivised star ratings cannot be disaggregated from the over all star ratings for a product.

“Consumers have growing distrust and even disdain for incentivised reviews, especially when it seems every single one is a glowing five-star review,” said ReviewMeta, which analysed 7m Amazon product reviews to determine the extent of bias of incentivised reviews.

“We found that reviews containing language that would indicate the reviewer received the item for free or at a discount in exchange for a review (incentivised reviews) on average rate the product .38 stars higher than reviews that did not contain this disclosure (non-incentivised reviews).”

Isolating those that had at least 10 incentivised reviews and at least 10 other reviews produced a sample of 609,766 reviews, which also showed a positive bias of an average 0.29 stars.

ReviewMeta found that incentivised reviewers were 12 times less likely to give a one-star review and four times less likely to leave any kind of critical review. The volume of incentivised reviews is increasing sharply, making up the majority of new reviews on Amazon since February.

While increasing the star rating of a product by only 0.38 points may seem small it could be enough to propel a product from the 54th percentile to the 94th percentile, according to ReviewMeta’s data.

“Considering that the average product on Amazon is rated around 4.4 stars, a boost from 4.36 to 4.74 stars can mean the difference between a mediocre product and a top rated product,” said ReviewMeta.

Many incentivised reviewers of products are members of so-called review clubs, which organise and facilitate product exchanges. These reviewers typically appear to review many different products giving very high or five-star ratings to each product.

ReviewMeta said: “Incentivised reviews are a new and rapidly growing breed of review. While some people label them as ‘fake’, incentivised reviews don’t technically deserve it because they are likely from real people who had a real experience with the actual product. However, the data still shows they still have a bias – despite their claims to the contrary.”

ReviewMeta’s analysis did not include Amazon’s similar Vine review system. Amazon did not immediately respond to request for comment.