Online marketplace Amazon has placed a limit on the number of reviews shoppers can leave on the site.
In a bid to put a stop to false feedback, people can now write only five reviews a week of items not bought via the online store.
The change applies to most products and is part of efforts to clamp down on people selling positive comments.
The change is Amazon's latest step in its battle to ensure users trust its listings.
Users can still review as many items as they like if the goods are purchased via the website.
"The change makes a lot of sense. There has been a massive clampdown on fake, bogus and heavily influenced reviews recently," said Patrick O'Brien, retail analyst at Verdict Retail.
In October, Amazon announced the end of ''incentivised reviews".
While direct compensation for reviews had never been allowed, there was an exception - reviewers could until last month post a review in exchange for a "free or discounted product as long as they disclosed that fact", according to Amazon's website.
Now, that has changed. Such reviews can appear on the site only via Amazon's own program, Vine.
Five's the limit
Amazon published its updated rules in its Customer Service section.
"You can submit five non-Amazon verified purchase reviews each week, starting on Sunday," it says.
Amazon also reserves the right to restrict reviews of certain products to users who have bought it via the site if "unusually high numbers" of reviews are submitted in a short period of time.
"Amazon's review system is very impressive in terms of the volume of reviews there, it's far superior to those of competitors," said Mr O'Brien.
"The new rules will make it very difficult for people who are trying to make money by selling fake reviews. It does show Amazon is taking this matter seriously."
The new rules will not apply to books.