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The real impact of fake reviews

Key Findings

  • Using a behavioural experiment with almost 10,000 participants, we found that fake reviews had a strong impact on consumer choices, leading many away from choosing high quality products and towards a Which? Don’t Buy.
  • When the star ratings and review text of the Don’t Buy were manipulated, consumers were more than twice as likely to choose it as the option they liked best.  This increased even further when a platform endorsement was added.
  • Warning consumers and giving tips on how to spot fake reviews did help as 20% fewer people chose the Don’t Buy.


Many consumers rely on online customer reviews to help them decide what to buy, but unfortunately these cannot always be trusted. Which? investigations have found thousands of fake reviews across a variety of well-known online platforms.

These fake reviews risk creating harm by leading consumers into unwittingly buying poor quality or value goods and services. And in the worst cases products which are counterfeit or unsafe. 

However, evidence has been lacking on the extent to which consumer decisions can be manipulated by fake reviews and the level of harm this causes. To address this, Which? worked with the research consultancy, The Behaviouralist, to produce innovative research into how consumer behaviour changes in the presence of fake reviews. The full report on the experiment can be found here.

Fake review treatments

We found that all the fake review treatments we added significantly increased the likelihood of a consumer choosing the Don’t Buy product as their favoured option. In the control group, where the participants did not see any fake reviews, we found that 10.5% chose the Don’t Buy as their preferred option.

When we inflated the star rating of the Don’t Buy product to mimic the effects of large-scale review spamming, this led to a 5.8pp increase in choice over the control group.       

When this inflated star rating was combined with faked review text mirroring the language and other features of fake reviews we had encountered in real life, we found an increase in choice of 12.6pp over the control group – an effect size of 120%. Even when we included additional signs of suspicious activity in the review text, like admissions of incentivisation, we still found that more than twice as many participants chose the Don’t Buy compared to the control group.

Load infographic

Platform endorsements

Adding a platform endorsement on top the fake review treatments increased the proportion of participants choosing the Don’t Buy by a further 1.7pp, representing a 135% increase in choice over the control group. This suggests that where such endorsements are linked to fake reviews they could be effective at amplifying the harm.

An effective warning?

Finally our experiment explored a simple remedy that could reduce the harmful effects of fake reviews. We included a warning banner at the top of all the shopping screens that the participants could see – both the search pages and all product pages – warning of the potential presence of fake reviews and some tips on how to avoid them. Consumers who were shown this banner alongside the fake reviews and platform endorsement were 20% less likely to choose the Don’t Buy product, reducing the harm. But this is still around 80% more than the control group who didn’t see any fake reviews at all. This suggests that while warnings might reduce the harm from fake reviews, preventing such reviews from appearing in the first place should be the priority.

Published 17.06.20

Contact us

If you have any questions or would like to find out more, please email us at consumerinsight@which.co.uk 

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