Word of mouth is an amplification mechanism that also filters. It seems silly to imagine a product spreading by word of mouth because of how bad today’s products often are. Rather than having to earn spread through appeal, companies can pay money to shortcut the process. In an advertising-less world word of mouth would carry farther because the products would adapt to the filter to be better. It would probably take awareness plenty far to enable a business owner to tell you, 4-6 hops away, about his/her innovative new vacuum or whatever.