Not everyone is a sophisticated Yelp user with an understanding of social networks. A lot of people will simply see two 5-star reviews, zero negative reviews, and think that looks like a safe bet.
Are you saying it's Yelp's responsibility to protect unsophisticated users from themselves? Also, I am not quite sure "a lot of people" will behave as you describe.
If one has to become a sophisticated Yelp user and do a substantial amount of detective work in order to determine if Yelp reviews are legit in order to get any value out of it (or at least not get actively misled by it), then what value does Yelp provide?
