GSI Commerce’s marketing services unit has made its first acquisition under Chris Saridakis, who was hired away from Gannett ( NYSE: GCI ) to run it in mid-April. GSI Commerce—which offers a suite of services to e-commerce retailers—is buying retargeting startup FetchBack , which lets sites deliver targeted messages to visitors after they have left. In a release, Saridakis claims “retargeting is far more effective than traditional display advertising” and says the acquisition is part of a “strategy to expand GSI’s marketing services capabilities,” which already include e-mail marketing and a full-service digital agency.