Fed up with business owners paying for fake reviews, Yelp is to introduce a system to warn users when it believes they’re being misled.

It plans to place a Consumer Alert, triggered by the company’s automated review filter, on the pages of businesses it thinks are dodgy, telling users that the company’s been caught trying to buy reviews.

Currently, of the company’s 30 million reviews, one-fifth is determined to be possibly inauthentic and relegated to a secondary page. Some criticize a competitor, while others are self-reviews or generated by paying fake customers.

“This pretty much breaks every rule in the book, not to mention it’s just wrong to mislead consumers with fake reviews,” says Eric Singley, Yelp’s vice president of consumer products and mobile.

Yelp’s playing it safe, and has so far placed an alert on only nine business entries, from a total of around 20 million – but says it plans to post more on an on-going basis. They’ll be removed after 90 days, unless Yelp finds further gaming is still going on.

In future, the company plans to incude more information in the alerts.

“Beyond alerting consumers to attempts to purchase reviews, the next step will be to let consumers know if a business has had a large number of reviews submitted from the same Internet Protocol (IP) address, which can be a helpful indicator that they lack authenticity,” says Singley.

“While the review filter already takes this type of information into account, we believe that consumers also have a right to know if this activity is going on.”