Word of mouth is an amazingly powerful force — but how does it really work?.Businesses have become obsessed with stimulating word-of- mouth to counteract the declining effectiveness of advertising. But it's easier said than done.As the founder of BzzAgent, a community of more than 400,000 people who volunteer to talk to friends and acquaintances about products they genuinely love, Dave Balter is a successful practitioner, not a theorist. And he's figured out how to measure and harness word-of-mouth without corrupting it.In Grapevine, Balter shows why honest feedback – about books, restaurants, gadgets, or anything else – is more believable than any paid endorser. And he answers some of the most elusive questions in marketing, such as what makes word-of-mouth very different from "buzz" and "viral marketing."