It's possible the sketchiness is caused by a restaurant's competitors (writing negative reviews, falsely flagging positive reviews, spamming) rather than Yelp proper.
That adds a bit more complexity to the problem, but it still remains that Yelp is running a platform that to some extent relies on the ability to abuse it.
There is an enormous gulf between a platform with abusive users and a platform where the operator uses it to engage in extortion.