I'm not claiming this evidence is conclusive (I haven't looked at it closely enough), but it's worth being aware of before making accusations like that.
I only read the abstract of that paper, but it doesn't address the extortion. It only addresses _user_ fraud, such as leaving a bad rating on a competitor.
It doesn't address the fact that Yelp can manipulate reviews however they please, as the court ruled.
I'm not claiming this evidence is conclusive (I haven't looked at it closely enough), but it's worth being aware of before making accusations like that.