Up to 50% of online product reviews are fake according to industry experts.
Five-star reviews which are highly sought after by sellers are often bought or written by family and friends.
That is the verdict of Andrew Levi, founder of Capo Commerce, a company which helps firms boost their e-commerce presence with genuine reviews.
Fraudsters use false reviews to influence consumers to buy sub-standard goods and services or even dodgy counterfeits.
These firms will write reviews themselves or bribe others with cash payments for every positive review they post, according to a report in the Mail on Sunday.
Nine out of 10 people admit reviews influence their buying habits and strong recommendations can boost trade by at least 25% said Levi.
READ MORE: Matalan moves to sell off HQ
This means phoney reviews are big business in the UK's £23bn ($29bn) a year online shopping marketplace.
"Positive reviews to a seller are like gold dust. Buyers place a heavy weight on what is posted by other customers. Companies know that if they can manipulate these comments it will be good for business. As many as 50% of all reviews are now fraudulent," Levi told the Mail on Sunday.
Online traders can buy fake reviews from £1 and websites such as BuyUSAservice and Social Media Badge Verification also advertise five star review services. This can cost up to £50 for 10 excellent reviews.
This type of misleading practice is illegal under the Consumer Protection from Unfair Trading Regulations 2008 and traders can be blacklisted if they are caught using fake reviews.
Online shopping giant Amazon (AMZN) has pledged to fight fake reviews and in 2019 took legal action against companies selling four and five star reviews.
But consumer watchdog Which? has called on the tech firm to "takes stronger action to ensure people can trust the information they see online and aren’t duped into buying poor quality products."