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

Convincing speakers vary their speech when they speak for different purposes and to different people because different people have different interests and they look for different things when they are listening to someone speak. For example someone who is selling sports goods would talk differently to those people who are athletic compared to those who are not as athletic and might be trying to try something that will get them to be active and are trying something new.