Undercover marketing targets potential customers by concealing the commercial nature of an apparently social transaction. In a typical case an individual approaches a marketing target apparently to provide some information or advice about a product in a way which makes it seem like they are a fellow consumer. In another kind of case, a friend displays a product to you, and encourages its purchase, but fails to disclose their association with the marketing firm. We focus on this second type of case and argue that the constitutive dispositions of friendship which provide for the development and maintenance of intimacy also render friends especially vulnerable to undercover marketing techniques and so to the exploitation of friendship for commercial ends. We show how this is corrupting both of the friendship and the commercial agent.