When you ask this question, people immediately turn their focus on business related one. However, the truth is these 3 words might NOT related to each other at all, for example:
"distributor" can be part of engine, in Chinese, it is called "配電盤"
2014-09-30 13:37:52 補充：
"dealer" can be used to describe a person, like "a plain dealer" (質樸的人)
"agent" can be used as herbicides, like "agent orange" (枯葉劑, American used it in Vietnam war)
Fro the above examples, you can see, they are necessary related to each other.
2014-10-01 11:53:41 補充：
they are necessary related to each other.
==>they are NOT necessary related to each other.