Yelp has many easy opportunities to be a shady company and raise its profit margins in ways that are 100% invisible. For example, they could claim that an ad impression got twice as many views as it actually did and there would be no way to call them on it other than a few internal potential whistleblowers.
However, running a blatant extortion scheme where there is inherently a huge paper trail is not one of those things. Any one of the millions of businesses could become a whistleblower simply by posting an email to Hacker News, and Yelp would go from a near billion dollar company to a fraction of that.
It saddens me that if someone accused my startup of doing something absolutely atrocious, illegal, and irrational, instead of giving me the benefit of the doubt, it looks like Hacker News would actually say "where there's smoke there's fire" and start to rationalize how I am likely guilty given zero evidence.