BzzAgent, a Boston-based startup, specializes in creating word-of-mouth campaigns for big companies such as Unilever, L’Oreal and Michelin. The company enlists over 800,000 people in the U.S. to try out certain products, which they can choose to write about to their Facebook friends or Twitter followers. The company does not pay any of its consumer volunteers, and they are not required to say anything about the products.