I am unsure of reviews.
PPC is still in its infancy (in my opinion). Google and other search engines including services such as Facebook, Yelp and several others, change their methods of search ranking and other aspects so I feel like all the PPC and SEO companies have to react to the changes. That results in a lag time for customers who rely on results of PPC for walk-in and new client trial business. It's a bit of "that looks about right...for now".
Expectations set by the vendors can be all over. It's part of the negotiation and contract you get into. There is no one thing that works.