A basic element of persuasion is the speaker: what do we think about the speaker? Aristotle called this element of persuasion, ethos (like ethic).

Dr. Flynn of McMasters University argues that Aristotle’s ethos, the way in which we perceive the speaker functions as a heuristic, a means of peripheral route processing which leads to greater and easier reception of the message. The responsiveness of the hearer to speaker depends upon a number of elements in the speaker and in the hearer.

On the speaker’s side, Flynn identifies trust, authenticity, credibility, expertise, attractiveness. Now it is true that the hearer is the one who bestows trust and such upon the speaker. The hearer must believe the speaker to be trustworthy or credible. But the quality is something which is perceived to exist in the speaker.

The fact of trust, for instance, immediately creates a basis to receive the message from the speaker. If I trust you, I’ll listen to you.

The converse is thus obviously true, if I do not trust you, there is no reason to give you my attention. But what if I am merely ambivalent: I’ll give you a listen, but I don’t know that I would take advice from you. In that instance, the heuristic won’t act to shortcut the decision making. I’ll need to stick around.

Authenticity is the degree to which I will allow the current statement to be integrated with my I previously believed about you. I see a celebrity influencer speaking day after day about the greatness of this product. I have seen the celebrity tout this product for years and speak of personal use. I believe the celebrity actually uses this product. But then one day, the celebrity hawks a competing product. It doesn’t sound right to me
Expertise: You have been my doctor for years; I trust everything you have told me about medicine. Then one day you begin to offer your opinions about macro-economic policy. How do I receive that? I could think you’re pretty smart. I could think, you’re a doctor, how to you think you can talk about economics.

Credibility. Do I believe you? Obviously if I do not I will not confer trust upon you. If you need an example, look to how your friends perceive the public statements of a politician from a disfavored political party.
Attractiveness. This involves physical attractiveness, but is not limited to physical attractiveness. It is well known that jurors are more likely to believe physically attractive witnesses.

He also identifies two characteristics which are perceived to belong to listener: identification and expectations.

We in the end have a tribal default switch. When the speaker is someone I perceive to be like me, I’m more likely to believe that speaker. There is an observations among political consultants is that the winner is the one most people could imagine having over for a barbeque.

Finally, I’m only going to trust a speaker who says something which I could have potentially already believed. I come to a lecture and the person behind the podium beings to speak on and on about the hidden world inside the hollowed earth and how aliens and dinosaurs secretly live beneath us now. I am unlikely to grant much in the way of sympathy for the speaker’s views on anything else.

Terence (Terry) Flynn, Ph.D., You had me at hello: How personal, developmental and social characteristics influence communicator persuasiveness and effectiveness
Research Journal of the Institute for Public Relations 1 Vol. 3, No. 1 (August, 2016), 1-11