paseoyelpCyber-shilling” is already well-known in the online review space, when people are paid to write faux reviews for products or places.

But a new study from MIT shows that these aren’t the only phonies being published. In fact, five percent of the negative reviews you read are actually penned by loyal customers of a brand who haven’t actually bought the products or used the services they are writing about.

MIT Sloan professor Duncan Simester and Northwestern University researcher Eric Anderson co-wrote a paper titled “Deceptive Reviews: The Influential Trail” that examined how and why these hardcore fans are essentially lying via the Internet about brands they love.

“These findings suggest that the phenomenon of deceptive reviews may be far more prevalent that we would otherwise think,” Simester said.

The researchers examined reviews for a private-label apparel company that only allowed submissions from registered users. Because of this, Simester and Anderson were able to compare purchase histories with usernames.

They found that five percent of those reviews were written by people without any purchase history of the specific product, but a long history of purchases from the company. Their postings, which tended to be longer than normal and usually contained details unrelated to the product, were also more negative than the other 95 percent of which were composed by actual buyers.

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Simester and Anderson, who replicated this process with book reviews at Amazon, came up with two possible explanations for this. The five percent who posted fake reviews could be “acting as self-appointed brand managers.”

“They really like the company, but then they see it selling a product or doing something else they don’t approve of,” Simester said. “They post the reviews as a way to give feedback to the company about how to improve their performance. They will even do so on products they have not purchased.”

The other explanation was that the reviewers want to show how knowledgeable they are about a product and beef up their online ego by demonstrating their expertise.

Regardless, this isn’t good for companies.

“It may now extend to individual customers who have no financial incentives to write counterfeit reviews,” Simester said of the phenomenon of deceptive reviews. “And if this is true, we’ve increased the scale of the problem enormously.”

Previously on GeekWire: Yelp’s new Word Map feature shows you how to avoid all the hipsters in your city

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