Fake online reviews are being openly traded on the internet, a BBC investigation has found.
BBC 5 live Investigates was able to buy a false, five-star recommendation placed on one of the world's leading review websites, Trustpilot.
It also uncovered online forums where Amazon shoppers are offered full refunds in exchange for product reviews.
Both companies said they do not tolerate false reviews.
In 2016, Amazon introduced a range of measures prohibiting what it called "incentivised reviews", where businesses offered customers free goods in exchange for positive reviews.
"5 star is better for us" said one person making such an offer, in an exchange of messages with the BBC.
5 live Investigates is on BBC Radio 5 live, 29 April at 11:00 GMT - catch up on BBC iPlayer Radio. »