"Worth mentioning is Yelp's long (alleged) history of using review filtering as a de facto racket to 'encourage' businesses to sign up for their paid services."
EXTREMELY worth mentioning. If you've yelped Yelp, so to speak, you know to take their recommendations with a grain of salt and then some. Caveat emptor.
While I'm on the topic, the idea of a single company managing reputation for any given space is silly beyond words. Downright moronic, even.
Reputation is an aggregation of multiple opinions. No aggregating entity can aggregate without their aggregating principle spinning the results. Yelp is notorious for a corrupt and indeed outright criminal aggregating principle -- "we'll suppress bad reviews if you pay us and good reviews if you don't" -- but the same is true for any aggregator, whether they're aggregating based on good principles or bad, because aggregation is a form of authorship. I mean look at Hacker News vs Reddit vs Digg vs Slashdot. They all aggregate, and each has a distinctive voice.
Because of this, yes, Yelp is a useful resource, but no, don't use it for a serious purchase without going on Google. If you use Google and Yelp, you're at least polling multiple sources, so you're doing something which can access the fundamental aggregating dynamic which powers reputation in the first place. A single point of failure for reputation is a contradiction in terms!