Maybe not outright extortion but certainly not what they claim of being a truly independent forum.
An environment where salespeople feel they can do stuff like that is a problem, but no, it is not proof that "yelp deleted bad reviews for money"
Yelp definitely hides a lot of reviews that are completely legitimate supposedly due to their review validity system filtering them, but in a lot of cases I've seen the only crime these disenfranchised reviewers had was that they didn't want to go make a full-blown Yelp profile with pictures and everything to make really serious, very well described complaints. This artificially inflates review relevancy ratings for companies that have Yelp reviewers that skew towards younger demographics. There's a ton of stores where I live that are frequented primarily by 50+ year olds but they have almost zero Yelp presence since nobody operating or visiting the store are much into technology / social media enough to care.