Amazon is cracking down on inaccurate product reviews by banning any that were "incentivised," except—that is—for those that come from its own Amazon Vine program.

Until now, Amazon allowed businesses to offer products to customers in exchange for a review, provided the affiliation was disclosed in the text. It's common to see something like "I received this product for free or at a discount in exchange for my honest, unbiased review" while browsing the site. Unfortunately, while some incentivised reviews may be authentic, many tend to be overwhelmingly positive. For shoppers looking for accurate reviews on potential purchases, this is a big problem.

A recent study of over seven million reviews by ReviewMeta found that incentivised reviews (those that contained some kind of disclaimer text) were rated 0.38 stars higher than non-incentivised reviews. That might not sound like much, but even with this small bump, products could be boosted from the 54th percentile to the 94th percentile, effectively creating a "Top Rated" product. The study also found that incentivised reviewers were 12 times less likely to give a 1-star rating and nearly four times less likely to leave a critical review.

"Consumers have growing distrust and even disdain for incentivised reviews, especially when it seems every single one is a glowing five-star review," ReviewMeta said.

While Amazon isn't removing older incentivised reviews, except for those it deems particularly excessive, it will now take action against any companies found distributing products for free in exchange for reviews. The online retail giant has taken a zero-tolerance stance to outfits found violating its rules before, suing companies that directly pay for fake reviews, and in some cases even suing the individuals that write them.

"Any attempt to manipulate Community content or features, including by contributing false, misleading, or inauthentic content, is strictly prohibited," reads Amazon's updated community guidelines. "If you violate our Guidelines, we may restrict your ability to use Community features, remove content, delist related products, or suspend or terminate your account… Misconduct may also violate state and federal laws, including the Federal Trade Commission Act, and can lead to legal action and civil and criminal penalties."

The only exceptions to the new rules are books—Amazon will "continue to allow the age-old practice of providing advance review copies"—and reviews that come from the Amazon Vine program. With Vine, Amazon (not the vendor or seller) asks reviewers to post opinions about new and pre-release products and does "not incentivise positive star ratings, attempt to influence the content of reviews, or even require a review to be written." It also limits the total number of Vine reviews displayed for each product.

"Vine has important controls in place and has proven to be especially valuable for getting early reviews on new products that have not yet been able to generate enough sales to have significant numbers of organic reviews," Amazon claimed. "We also have ideas for how to continue to make Vine an even more useful program going forward. Details on that as we have them."

Amazon isn't the only company to have cracked down on dodgy user-generated reviews of late.

Valve recently changed its review system on Steam so that reviews written by users who received a game via a developer- or CD-distributed licence key would no longer count towards the review rating. The change also affected reviews from Kickstarter backers that received a Steam key as part of a backer reward.

Unfortunately for Valve, the change resulted in backlash from Indie developers, particularly those that saw success on Kickstarter. It has since partly dialled back the changes, with the review section on each product page showing reviews written by all users, regardless of how that game was purchased. However, while reviews from non-Steam users are now easier to find, they still don't have any impact on a game's overall review score.