The article says she asked her customers to post genuine reviews. I don't know if that's true but if it is, I see nothing shady about asking your customers to post reviews. There is definitely a conflict of interest on Yelp's side, but I don't see a good solution to the spam problem.
Both things can be true: that Yelp has and exploits a conflict of interest, and that this article chose a pretty bad example of a business harmed by that practice.
Yelp specifically mentions that this would lead to blacklisting of comments in their help, for the reasons of resulting bias (you only ask customers who are happy, you might provide a discount or preferential treatment etc).
