The "Reliable" Speaker

A couple weeks ago in class we discussed the "reliable narrator." I was thinking about this idea while living my daily life.  I realized this is something that people are judged on all the time when they are speaking, if not every single thing they say.  It is not only being a "reliable narrator," but being a reliable speaker as well. When listening to person talk, others are always deciding whether that person is reliable or not.  Are they speaking under self-interest, outside influence, inexperience, or ignorance?  A listener had to interpret a person's speech and think about if they can truly believe what they are saying.  I know that I definitely do this whenever I am listening to someone.  Do you think that when you listen to people around you, you are deciding whether or not they are a reliable source?