We've witnessed this manipulation first hand. My son used to go to the local day care that had stellar reviews on Yelp - 4 or 5 stars with a single 3 star revie

We've witnessed this manipulation first hand. My son used to go to the local day care that had stellar reviews on Yelp - 4 or 5 stars with a single 3 star review. I knew the vast majority of reviewers because they were parents whom I've met through kids birthday parties and the like. Then one day Yelp called the owner of the daycare asking her if she'd like to purchase some advertising. She already had plenty of business so she politely declined. A week later 20-something reviews went into "Not Recommended" category, effectively becoming hidden. The only review that remained on the site for the business was the single 3-star review. This is effectively extortion. In other words yelp won't fabricate reviews, it'll just selectively filter reviews if you don't pay them to pain a worse picture of your business.