Is there a straightforward way to monetize the review business without resorting to what's essentially extortion (BBB, Yelp) or having a feature subsidized by other methods (Google reviews)?
It's all possible, but simply asking for $100 is a lot easier because the power disparity is so huge.
Then there is the fact that is Facebook ever shows interest they can easily crush the entire market - they don't need to make immediate money and the identity of the reviewers is better known, providing higher quality score.
That being said, I've heard everything about the ratings business is a lie, so there seem to be insiders claiming that there's a lot of fuzziness to the problem.
I'm assuming that manual curation of reviews is necessary here, it may not be.
The unfortunate side effect is you never end up learning which companies to stay away from, because a system like that only focuses on the good, but you need a system that benefits both buyers and sellers.
Also consider that customers themselves might have (non-algorithmic) reputation that will decide if/how they can affect the reputation of others. Pagerank, if you will.
The entire field is crying out for big data, but then drowns in big dollars.