To make sure that the services offered were legit, Amazon dispatched investigators to buy reviews. This led to the rather surreal situation where sellers would explain their strategies for evading detection by Amazon to a representative of Amazon.
This is different. Most of the time it is the dentist or business owner suing Yelp for malicious content. Now Amazon is trying to crack down on services offering bogus Amazon reviews for a fee.
This is just another indication of how powerful online reviews have become, yet they are very poorly regulated and the system as it now stands is corrupt and too easy to scam.
One source estimated that as many as 1/3 of online reviews are bogus.