The company Pfizer decided use a credible source to advertise their cholesterol-lowering drug Lipitor. Experts command a great deal of respect and possess the specific knowledge that laypeople cannot compete with. Therefore, using credible sources and experts can prove persuasive. A study by Maddux and Rogers' (1980) illustrates this effect nicely. They manipulated source expertise and found that expert sources had more influence than non experts. Participants agreed more (measured using an agreement scale) with a view about sleep if an expert’s (i.e. Doctor of Psychology and physiology) endorsed a certain argument, than when a non-expert (a Doctor of music) did. Because Pfizer’s product was medically related, who better than a doctor, an expert in the respective field, to endorse their product? They decided to use Robert Jarvik.
However, this advert ultimately proved unsuccessful. The reason for this was that an investigation into Robert Jarvik found that he never underwent a medical residency, and never obtained a license to practise medicine. This led to the ad being pulled and the campaign turning into a catastrophic failure. This is because the tactic of using an expert in a certain field to both endorse and describe a product cannot work if the expert used is in fact a fraud and possesses no expertise. Once his expertise is exposed (and undermined), the primary persuasion tactic has disappeared, and the result is that the advert does not possess the necessary tools to be effective.
Thus, the advertisement perhaps would have worked if a fully licensed medical doctor was used instead
Maddux, J. E., & Rogers, R.W. (1980). Effects of source expertness, physical attractiveness, and supporting arguments on persuasion: A Case of brains over beauty. Journal of Personality and Social Psychology, 39, 235-245.