Tupperware Home Parties, Shaklee Corporation, Amway, Mary Kay Cosmetics--theirs is an approach to business that violates many of the basic tenets of modern American commerce. Yet these direct selling organizations, fashioned by charismatic leaders and built upon devoted armies of door-to-door representatives, have grown to constitute an $8.5 billion a year industry and provide a livelihood for more than 5 million workers, the vast majority of them...