J.D. Power III, that arbiter of quality and customer coddling, is a director of Driver's Mart Worldwide, the Grand Rapids, Mi-based consortium of mega-dealers looking to compete with Circuit City Stores Inc.'s CarMax in the ultra-hot used-car megastore mania. Isn't that a little like inviting the professor to your study group? Sales people will be paid a fixed salary, prices will be non-negotiable and the atmosphere will be low-pressure. Still, imagine the howls from dealers when Driver's Mart scores at the top of a J.D. Power and Associates study of used-car dealers' customer satisfaction. "Mr. Power would never do anything to jeopardize our credibility or the evenhandedness of the research we do:'says Patricia Patano, a spokeswoman for J.D. Power. "Although he is a director, his real role will be as a consultant'" What's that line about consultants telling the client what he wants to hear? Just wondered.