The lack of transparency isn't surprising to me, as that's basically industry practice when it comes to the "special sauce" algorithms that power these recommendation engines (google, tripadvisor, whoever).

But the extortion part does surprise (horrify?) me. I'd love to see some more concrete proof that advertising on yelp results in a friendlier filter function for that business. I assume that there is enough publicly available information (just by scraping their site) to establish some kind of correlation between advertising and filter-friendliness, if one exists. Any of you up for the challenge?

I'd settle for seeing those communications w/the sales team referenced in the article, though.