Blackmail notwithstanding, what was the $300/month meant to be for? How do they rationalise it?
You read a LOT of Yelp blackmail stories (or I have). But it isn't clear what legitimate product they're actually selling to businesses, since they'd at least need a cover.
PS - I am surprised any business has less than five reviews. If I ran a small business, I would create fake reviews just to get the ball rolling, no matter how immoral that is. Just makes good business sense.