We fumble around Yelp before deciding where to grab grub, re-reading reviews of neighborhood haunts to remember which burger, burrito or baklava is best.

We methodically compare product reviews before splurging on a new smartphone, digital camera or flat screen TV.

Marketing professors Duncan Simester of MIT Sloan and Eric Anderson of Northwestern University, however, would caution: “Stop wasting the time.”

 A study from the duo recently surfaced, highlighting the prevalence of fake reviews. There’s long been speculation of “cyber-shilling,” the practice of companies posting negative reviews of their competitors’ products, or businesses rewarding users to write glowing reviews of their own. But new research shows even the most loyal of customers are publishing negative remarks about goods they never even purchased.

Results are based on reviews from a prominent private label apparel company, boasting hundreds of thousands of product reviews. What the pair found is that roughly five percent of the reviews written were penned by people for whom there was no record of having purchased the product. What’s more, those five percent were more negative on average than the other 95 percent submitted by individuals who had actually bought the item.

Shirk off the statistics, but the fake reviews do have consequences. Low ratings result in significantly less demand for an item for at least a year, according to the Portland Press Herald. Simester and Anderson were actually able to replicate the effect using book reviews on Amazon.com.

Although it remains unclear as to why customers would post critical reviews of products they didn’t buy, the two offer up suggestions.

One is that they may be acting as “self-appointed brand managers,” according to the study, meaning users see the reviews as a way to give feedback to a company about products, regardless of whether their feedback is fake. The second is that they might be looking to raise their online social status by posting with great frequency or detail to appear as though they have expertise in something.

Below is an example of what to watch out for from Simester and Anderson’s study.

(h/t Boston Business Journal