There are many variables which affect the likelihood of thinking about the merits of a message and thus the route to persuasion. These variables affect a person's motivation to think about issue-relevant information and the ability to do the cognitive processing. While, other variables affecting motivation are part of the person and the situation. One commonly used technique of persuasion is that of authority. This is based on the idea that people will respect the opinions of someone who is assumed to have a lot of knowledge about the product.
People feel better knowing that someone with authority has recommended what they are about to buy.
Of course, the authority person has to have expert knowledge in that particular field. One way in which it does this is by appealing to your emotions. It can arouse feelings of fear, love, pleasure, or vanity. Scarcity is the fear that you may miss an opportunity to purchase a product. Health advertisements often utilize fear to get the audiences' attention.