I am in the process of create a site, but I am having a problem coming up with a proper review system that works. Here is an example, lets take Yelp.com is has businesses where people review businesses. Lets say I am owner of a business and my competitior who is across the street also is on Yelp. How does Yelp prevent me from creating fake accounts and giving bad reviews to the competition purposly even though they never bought anything there and also create fake accounts to give themselfs good reviews? I know people might say o IP block and stuff like that, but using different computers and even when you are on 3g/4g on your phone every 10 feet you move you ip address changes. So person can be walking around his block and register 20 accounts and give bad reviews to competitor and give good ones to them selfs. Whats a good creative way to block that? Thanks in advance for the help.