Once trust has been established, it is much easier to build the second pillar of credibility – expertise.

In one experiment carried out at an Australian university, a man was introduced as a guest speaker from Cambridge University in England. However, his expertise was represented differently to each class. To the first class, he was introduced as a student, to the second class as a demonstrator, to the third class as a lecturer, and to the fourth class as a senior lecturer; to the fifth class, he was introduced as a professor.

After each class, the students were asked to estimate his height. Remarkably, with each increase in expertise, the same man grew in stature by an average of half an inch. As a "professor," he was ...

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