My friends who own or help run local small businesses have told me it happened to them, so I believe my friends. Of course, it's not explicit extortion like "pay us $500 a month or else", so there's no hard evidence for anything. Instead, magically not too long after they refuse a cold-call sales pitch, they have a bunch of bad/fraudulent reviews surface to the top of their Yelp page and then get another sales call later on.
Numerous credible reports from business owners, and numerous denials from Yelp. I don't really know who to believe.
I would hardly call them credible reports. It's easy to see how business owners could draw false inferences when they receive a Yelp sales call and coincidentally get a negative review shortly after.
Honestly, I thought this was long since debunked. There is no physical evidence of Yelp sales execs extorting small businesses.
Simply put, no. No evidence other than hearsay. And this, after countless lawsuits.