“The lack of transparency around agencies’ practices came into the limelight last month after a former Mediacom chief executive claimed that rebates are widespread across the advertising industry.  The allegations sparked a fierce debate about the trust between agencies and their clients, and now one analyst is warning investors to also take pause.

Pivotal Research analyst Brian Wieser on Monday downgraded his ratings on the four major ad holding companies — WPP, Omnicom, Publicis and Interpublic — noting that the allegations about ‘kickbacks’ in the U.S. are difficult to ignore. He wrote in a research note that there is a growing perception among marketers that agencies have been misleading about their media practices ‘without clients’ full understanding or support.’ Wieser reduced his recommendation on Interpublic to  hold and cut Omnicom, Publicis and WPP to sell.”