One of the biggest tricks used out there is allowing only the good reviews to be seen while flushing the bad to an email for the owner. That sounds great, but it’s not something Google allows. I am sure you already know what it's like to see stuffed reviews that are all great - but far from trustworthy.
With Yelp making it tougher to stuff the review box, Google knows it must keep close and has recently started to top Yelp. Don't forget Facebook, they too are getting in the game.