According to Bing Liu, a data-mining expert at the University of Illinois at Chicago, about one-third of all consumer reviews on the Internet are fake, that is, written by marketers or by third-party services such as Ad Blaze, whose website touts it will “write a professional review. ... Each [one] from a unique IP address located in the city of your choice. ... The reviews will be leaked at random times to look natural.” It guarantees that “your online listing will be safe and secure.”

Even if a review isn’t an outright fake, some disgruntled consumer — who might never have used your services at all — can still slam you. Minnesota home improvement contractor Terry Stamman discovered a negative review on Angie’s List from an unknown name and email address. He got in touch with the writer, for whom he had never done any work. It turns out she was angry that he wouldn’t come out to her house on a one-legger sales call. Although she removed her comments, a series of such negative reviews can do serious reputation damage.

On Angie’s List, users are paid members; they do get vetted. On Yelp, moderators don’t govern the site, but it has a reputation system among its reviewers and uses its own “filtering software” to weed out fake reviews — positive or negative. Cornell University has developed software to spot online fakes, and Yelp conducted a sting operation in 2012 resulting in a “consumer alert” badge to be placed on a business’s profile page if it is found to be using phony reviews.

The only way that fake reviews will stop is if consumers become educated or distrustful — a business that has all positive reviews should send up red flags. But with recent surveys showing that 72% of consumers trust online reviews, this issue isn’t going away anytime soon.

So what’s a company to do? Dan Wolt, owner of Zen Windows, in Columbus, Ohio, checks Angie’s List every day and alerts Angie’s if he doesn’t know who a reviewer is.

You can also choose not to engage with consumer-driven sites and focus on places where you have more control. “You don’t want to abdicate marketing responsibilities to a review site,” says industry consultant and REMODELING columnist Shawn McCadden. For example, GuildQuality, which does customer satisfaction surveys, converts those questionnaires to starred reviews that show up in search engines. A remodeling company can publish completed surveys to its Facebook or Twitter feed with links back to its own site.

Online review site leads should be part of a larger strategy. “You need a marketing plan, not just a list of tactics,” McCadden says.

—Stacey Freed is a senior editor at REMODELING. Find her on Twitter at @SFreed or @RemodelingMag.

The Rest of April's Cover Story:

Online Review Sites topic page

Necessary?Evil?: Online review sites are here to stay

Sites for Sore Eyes: Consumer-driven sites leave contractors no choice but to play the game

Site Guide: A quick guide to the dominant online review services

Optimized Engagement: SEO experts explain how reviews can boost your online visibility

I heart Angie (Not): Contractors' love-hate relationship with the online world's biggest player

Leading Lights: A shifting definition of what constitutes a lead

Friendly Recommendation: Word still spread quickly via the new wave of review sites that use media

Good Word: Why you should (or shouldn't) pay for positive reviews