When one of your business practices has a term coined especially for it by your customers it's probably time to question that practice.
The term in question? 'Hostage reviews'.
The CEO of Yelp, Jeremy Stoppleman, braved Reddit to answer questions. To give you a flavour here are the top comments...
The Yelp 'filter' is unique; that means one of two things: they're geniuses who have found a solution (in this case to 'dodgy' reviews - reviews written by competitors or the business in question, in the main) or the idea is flawed.
We think there is a solution, Mr Stoppleman. One that is fair to the businesses you are trying to sign up and equally fair to the businesses who politely decline your salespeople's offer.
Yelp is a community. Instead of the 'filter' (oh! - sorry, since 2013 Yelp don't use the term 'filter' any more, it's now calling the 'filter' 'recommendation software' - see here), allow anyone in the community (including all businesses) to flag up a review that they think is somehow flawed or tainted. Then employ moderators who can contact the reviewers and the businesses concerned to make a reasoned judgement.
Junk the 'filter' (sorry - 'recommendation software' is just such a mouthful) and replace it with human beings. You can afford them, and businesses are just too important to the economy to be randomly discriminated against by software that appears to be influenced by the need for Yelp's thousands of salespeople to have a ready bargaining chip when they phone small businesses.