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Scammers are making some restaurants an offer they can't refuse: A payoff or discount, or they'll post a nasty rating on online review sites like Yelp! or Angie's List.

There’s no real data showing how often it's happening, but anecdotal evidence suggests cyber-extortion is on the rise: scammers know online reviews carry a lot of weight, and can affect a company’s bottom line.

Some are willing to pay to keep bad reviews from popping up, but not Sonny Mayugba, owner of the popular Red Rabbit Kitchen and Bar in Sacramento.  He described how a patron recently tried to shake him down after alleging they got food poisoning.

"He said, 'I'm going to do a scathing review of you on Yelp!, I'm going to make sure my girlfriend does a scathing review on Yelp!, and then I'm going to report you to the health department. However, if you buy me a $100.00 gift card to Ella, which is a nice restaurant here in town, you'll save me from doing all those things.' To me, that was extortion."

Mayugba didn't pay a dime, and that customer's post -- while negative -- didn't mention anything about food poisoning, confirming the owner's suspicion the allegation was made up.

Legal experts say he was wise not to pay, or -- to file a lawsuit. They say if a business is seen as litigious, that can cause just as much damage as a negative review. Free speech advocate Matt Zimmerman, an attorney with the Electronic Frontier Foundation, says the better course is to use social media to explain their side of the story, and work even harder to earn more positive reviews.

"We can't control all speech about us, and we should stop trying," says Zimmerman. "Instead, we should try to encourage the positive feedback, try to encourage a more accurate picture of our business. Even if an ad or post is unfair, a business' more effective response is going to be to create a counter-narrative online."

Victim's of cyber-extortion can't blame the websites. Yelp!, Angie's List, and other review sites are not legally responsible for what their users do. However, if someone crosses the line, and posts something totally false intended to cause harm, that defamatory speech is not protected under the Constitution, and that person could be successfully sued. Attorneys suggest business owners track threats, collect evidence and report them to the police.

While the sites themselves may not be liable, most, including Yelp!, work hard to weed out sham posts, both positive and negative. From a business standpoint, it's in their best interest to try to screen out fake or malicious reviews if they want to maintain their popularity and integrity.

As Mayugba put it, a review site "is a wonderful sign post for those of us who use it correctly. When people use it to leverage value out of people for wrong, it devalues that media. That's not only extortion, but it's tainting the media platform."