Nineteen companies charged with writing fake online reviews were uncovered as the result of a year-long sting operation by the New York Attorney General. Offenders who posted fake reviews on Yelp, Google Local and CitySearch will be forced to pay upwards of $350,000 in penalties. As part of Operation Clean Turf, the AG’s office established a yogurt shop in Brooklyn and sought assistance from companies that boost online search results to combat negative reviews.

“Some search optimization companies offered to post fake reviews of the yogurt shop on sites such as Yelp.com, Google Local and Citysearch.com, the Attorney General’s office said in a statement on Monday,” reports Reuters. “The companies created online profiles and paid as little as $1 per review to freelance writers, some of whom were in the Philippines, Bangladesh and Eastern Europe, the Attorney General’s office said.”

“Other businesses, including family-owned bus company US Coachways Inc, a laser-hair removal firm, and an adult entertainment club were caught when managers, staff or friends wrote bogus reviews.”

Other businesses solicited individuals to submit fake reviews on classified advertising sites including Craigslist.com, Freelancer.com and oDesk.com.

“Commonly called astroturfing, employees of the 19 marketing companies would alter their IP addresses when creating reviews to appear as if each review was written by a different person,” notes Digital Trends.

AG Eric Schneiderman’s office explained that the fake reviews are in violation of laws against false advertising and deceptive business practices.

“Consumers rely on reviews from their peers to make daily purchasing decisions on anything from food and clothing to recreation and sightseeing,” Schneiderman said. “This investigation into large-scale, intentional deceit across the Internet tells us that we should approach online reviews with caution.”

Although Yelp’s shares fell as much as 9 percent, the company welcomed the crackdown and said it would continue to cooperate with law enforcement to combat fraud.

“In the long term it’s great because I mean there should be greater confidence in the consumers that the reviews are not being manipulated,” said Mike Hickey of Benchmark Co.