One of the strong points of persuasion is authority endorsements. This is when somebody who has some kind of authority or familiarity with a person, product, or service endorses that thing/person. From research, it is found that even if the person has personal benefits from the endorsement, it still helps persuade people when they hear the endorsement.
For example, when some football sports jock endorses a tennis shoe, everybody knows that he receives millions probably for the commercial endorsement. But none-the-less, many people will buy the product because they saw him endorse it. Even actors that nobody knows endorse products, and we understand that these are not “free-will” endorsements, but paid, and that most of the times, the actor or person talking has never even used that particular product before the day of filming.