How do convincing speakers vary their speech when they speak for different purposes and to different people?

They would say the benefits of what purpose they are speaking for and constantly talk without stopping with a nice understandable pace. They would focus more on the things that applies to the person that they are trying to pursue. Depending on what they are trying to pursue, they will give an example in action. Such as those who's selling make up, as they speak and commenting how pretty the product looks on the customer, they apply the make up on the customer's face. Even though when the customer is upset, they still would not say anything rude to the customer.