A few weeks ago, actor Jonah Hill suddenly started befriending a lot of novelists on Facebook. Most of them thought it was odd, but they accepted his friendship requests anyway. After all, it was Jonah Hill, right? Who wouldn't want to be his friend?


But then Jonah started doing something much odder: he started recommending another author's self-published horror novel. Not just once, but over and over again. It quickly became obvious that the Facebook Jonah Hill was not the real Jonah Hill. The Facebook account was shut down and the self-published author, who was masquerading as the actor, quickly disappeared.


Fake Jonah Hill is hardly the first fake name to endorse a product. These days, online reviews and product rankings are rife with outright fraud and ethically dubious behavior. Authors are paying for good reviews of their novels, companies are gaming the system by paying for five-star product ratings or leaving ratings themselves under fake names, and a new product review magazine even paid a research firm to prove that its product rankings were "better" than those generated by the venerable Consumer Reports. On the opposite side of the spectrum, some products get targeted by fake bad reviews, like a book about AIDS that was recently targeted by anti-circumcision activists.


The problem seems to get more and more pervasive every month: a recent survey found that by 2014 at least 10 to 15 percent of online product reviews will be fakes.


But at the same time, consumers depend on product reviews to make sure their money is well spent. "More than 60 percent of consumers read online reviews before making a purchase, and close to three-fourths trust online reviews from any source," says Andrew Schrage, co-owner of  the Money Crashers personal finance website.


So how do you know if a product review online is honest and trustworthy? "For customers, the best solution is to not trust a single site in isolation," says Mike Essex, online marketing manager for Koozai, a London-based digital marketing agency. "Check multiple sites for reviews and try to find a group opinion."


Brian Sheridan, development and marketing manager for the Council for Watershed Health in Los Angeles, says "the best way to trust a review is to look at the number of responses." The more good responses or replies a review has, the more likely it is to be real.


Another trick is to depend on sites that verify a customer purchased a product or service before they can review it. "I'm currently on a round-the-world trip and it's frustrating not being able to utilize services like TripAdvisor or the Lonely Planet boards without having to constantly be on the lookout for spam or lies," says Katy Cousins, who says she decided not to travel to Fiji because the local hotel reviews looked so suspect. "It's pushed me towards services like HostelWorld and Airbnb, because you can only review once you've actually stayed where you're reviewing. There is at least some measure of security."


A careful reading of a review may also reveal its veracity. "You may be able to spot a fake review just by looking at its wording," says Schrage. "I was recently reading some online reviews of a particular business, and one review had the phrase 'family-owned and operated for over 20 years.' What consumer would write a review with that wording?"


A product that only has five-star reviews might also send up a red flag. "There should always be a few negative reviews," says Robert Ian Mostyn, a web designer for the catalog company QCI Direct. "I only trust reviews when there seems to be a balance of them. Honestly for me, the first thing I do is read negative reviews."


Luckily, some companies have started responding to the threat of fake reviews. Google recently stopped linking to third-party reviews and is now encouraging people to write reviews using their Google+ identities. Many sites now allow you to report reviews you think might have been faked, helping to clear the air. "Yelp, Zagat, and TripAdvisor all aggressively investigate reviews in search of fakes, and a warning is posted next to the name of any business they suspect of having fake positive reviews," Schrage says. Even scientists are getting into the act, writing software that could soon help weed out fake reviews.


Ultimately, your best bet seems to be reading reviews with a healthy dose of skepticism and purchasing items only if you are comfortable with what you have seen online. "If you aren't 100-percent satisfied that there are enough real customer reviews," Essex says, "then vote with your wallet and don't buy a product."


Related social media story on MNN: Does your communication style depend on which social media site you're on?