Potentially fake reviews are flooding listings of tech products from "unknown" brands on Amazon, according to a Which? investigation.
Tens of thousands of overwhelmingly positive reviews were discovered from unverified purchasers - meaning they are much more likely to be fake.
In some cases, hundreds of five-star, unverified reviews were appearing on a product in a single day.
The analysis also found evidence of duplicated reviews, as well as positive reviews for completely different products being posted on a listing.
According to a separate Which? survey conducted last year, 97% of shoppers use online reviews to help decide whether to make a purchase - while the Competition and Markets Authority estimates £23bn of UK consumer spending per year is potentially influenced by online reviews.
Many of the "fake" reviews appeared on products made by brands that tech experts had not heard of.
Analysts say the floods of positive reviews could help boost listings for lesser-known brands so they appear higher up in searches on Amazon.
When researchers searched for "headphones" on Amazon and sorted the results by average customer review to find the highest-rated products, 100% of the results were "unknown" brands.
They also found 71% of products on the first page had a perfect five-star customer review score - and the majority of these reviews were unverified.
The British Standards Institute (BSI) has created a voluntary standard it wants businesses to adhere to in order to prevent customers being misled by fake reviews.
It says companies should verify that reviews come from genuine customers and moderators should be allowed to "flag" potentially fake reviews, among other guidelines.
In a statement, Amazon said it "invests significant resources to protect the integrity of reviews in our store because we know customers value the insights and experiences shared by fellow shoppers."
"Even one inauthentic review is one too many," it added.
"We have clear participation guidelines for both reviewers and selling partners and we suspend, ban, and take legal action on those who violate our policies."
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