The advertising industry has a dark past when it comes to the issue of source credibility. Each year, Gallup publishes their study of most- and least-trusted professions. Invariably, advertising practitioners rank among used-car salesmen and politicians right at the bottom of the list. (Sullivan, 1998, p. 4) Whether this nefarious reputation is due to mistakes made in the past or current practices is unknown. Whatever the case, the advertising industry shares an uneasy relationship with an American public that is both distrustful and wary of the practices used to gain their attention. David Ogilvy in his book Ogilvy on Advertising (1985) quotes a professor at the New School of Social Research who teaches his students that, "advertising is a profoundly subversive force in American life. It is intellectual and moral pollution. It trivializes, manipulates, is insincere and vulgarizes. It is undermining our faith in our nation and in ourselves." (Ogilvy, p. 206)

Clearly, there are those out there who do not believe advertising professionals are credible sources.

It for these reasons that a careful examination of the notion of source credibility is important for students of the advertising industry. Source credibility is an integral part of the persuasive process, one that can have a massive impact on the relative success or failure of a persuasive message. As Aristotle pointed out over two thousand years ago, a speaker’s integrity was "the most potent of all the means to persuasion." (Berquist et al., p. 35) Thus, in order for advertising messages to persuade in the manner in which they were intended, it is imperative that they weigh the importance of credibility.