Amazon is ending the practice of allowing customers to write reviews in exchange for free products.

It was previously allowed as long as the reviewer disclosed the fact that he or she had received the product for free.

A recent study of more than seven million reviews found that such reviewers were more likely to be favourable towards a product.

"These so-called 'incentivised reviews' make up only a tiny fraction of the tens of millions of reviews on Amazon, and when done carefully, they can be helpful to customers by providing a foundation of reviews for new or less well-known products," Chee Chew, vice-president of customer experience at Amazon, wrote in a blog post.

Such reviews will only be featured on the online store's own program, Amazon Vine, on which established expert reviewers new and pre-released items to help shoppers make informed purchase decisions.

Chew added: "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.”

Website reviews are hugely important to Amazon customers seeking the best quality products.

Last year Amazon sued four firms over the claim that they paid people to review products. 

Amazon has pledged to pay its seasonal employees in the UK well as it recruits 20,000 members of staff ahead of Christmas.

It was given the green light to test deliveries using drones in the UK this summer.