I doubt any business would fall for that since they already receive false complaints, bad reviews, negative reps etc from the new competitors who pay people to do just that.
I think you would be surprised. A lot of companies do pay off criminals like this, I know of a couple places I've worked at over the years that have done such. The thing is they never say it publicly so we are unaware of how often companies pay people off.
While I don't doubt that there are shady companies who pay to give compettitors a bad review, I don't think its THAT common. Typically if a restaurant is good it gets good reviews. Also these extortionists are threatening more than just bad yelp reviews....prank calls, phone ddosing, false orders, swating, calls to the BBB, etc etc. All of that combined can certainly be enough to convince a business owner to fork over $600 to make it go away.
A competitor paying for bad reviews isn't nearly as much of a threat. They are limited in what they can do without breaking the law and getting in serious trouble. Criminals aren't afraid to break laws so they have much more options at their disposal.