Sock puppet marketing is the use of a fake identity to artificially stimulate demand for a product, brand or service.
A fake identity created online for some deceptive purpose is known colloquially as a sock puppet. Sock puppet marketing is one example of astroturfing, the practice of artificially stimulating online buzz about something, while trying to make it appear to be a grassroots trend. In the case of marketing, buzz is created about a company, a product or a service to increase sales. Alternatively, sock puppets might denigrate a competitor or its product.
Sock puppet marketing and sock puppetry in general are unethical. Other compelling reasons to abstain include potential law suits and the damage to your brand that could occur as a result of discovery.
In this video, Google’s Matt Cutts explains the purposes and hazards of sock puppet marketing: