We have major news now. Do you ever look at online reviews for a restaurant or a contractor and did you ever hire one or go to the restaurant because of what you saw there? Well, move a little closer... See More
We have major news now. Do you ever look at online reviews for a restaurant or a contractor and did you ever hire one or go to the restaurant because of what you saw there? Well, move a little closer to the television because a sweeping investigation has found a large number of them are total fiction. Abc's chief business and economics correspondent rebecca jarvis has the truth. Reporter: We're using them for everything from planning dream vacations to choosing which doctors to visit. But according to regulators, a huge number of online reviews are complete phonies. Do you feel any sense of guilt or anything? Reporter: Um, no, because i feel like they'll pay someone to write a review anyway so it might as well just be me. Reporter: Kathy is 17 years old and says she's written hundreds of glowing reviews for four buts a pop and markets herself in this online video. I will bright a positive review of your website or blog or anything else you like. Reporter: How long does it take you to write a typical review? About three minutes. To write a review. Reporter: As many as 30% of the reviews you see online are complete fakes from restaurants to hotels to toys. And new york's attorney general is fighting back. They were paying or just ordering their employees and their employees' friends and families to write phony reviews to inflate their profile. Reporter: Getting a nod from your curious can seriously boost the bottom line. We've seen studies that a one-star increase on yelp can increase a restaurant's revenues by 10%. Reporter: Even yelp says it's a difficult battle. They tell us they will pay $50 to write a review. Yeah, we're subpoenaed a lot of these companies. This he keep popping up and we keep going after them but it's something that has to be dealt with in a coordinated way. Reporter: Do you have any reviews nearby that you could read to us. I made the appointment over the phone and the next day they were working on my bathroom. Reporter: Have you ever renn have aed a bathroom? No, I'm 17. Reporter: Cheerful about it, isn't she? So how do we spot a fake? I do it. I know I do it so how do we get smarter? We're all using these review, diane. You look for buzzwords like wonderful, great for everybody, the official product's name and anybody who says they're planning to do something or planning to buy it or use a service, that can be a dead giveaway that they were paid by the company to write the review. Planning to do it. Okay. Check online if you want to know more. Thank you, rebecca.
This transcript has been automatically generated and may not be 100% accurate.