Authority bias is the human tendency to attribute greater authority and knowledge to persons of authority (fame, power, position, etc.) than they may actually possess.
As an example, companies often use celebrities as spokespeople knowing that the audience will recognize this individual and give greater credence to what they have to say than an unknown individual. So think twice when you see an actor endorsing dog food and remember that he is not a scientist, a nutritionist, or a dog expert---he is a paid spokesman. This is also why in many advertisements for health treatments someone in a lab coat is promoting or encouraging the treatment - people view someone in a lab coat as being an authority and knowing what is right.