What are some tips for finding a reputable PPC management company?

According to the top 10 reviews website 2011's top PPC Management companies are as follows:&OrangeSoda, Silverback Strategies, Network Solutions, SEO.com, JumpFly, Inc., Evoba, isoTree, eBrandz, PPC, Management, ComCorp, Inc. OrangeSoda and sliverback both received Excellent review ratings.