Do you believe that a sales person who's successful in a certain field and products can be as successful in any other field and product range?

If a sales person has a desire to excel and also has perfect selling skills n him he can adjust himself anywhere.He just have to get product information though.

People are specialized in certain filed only. Or he will be successful in other product if they are sole agent only.

This is absolutely possible at all. Subject to the condition where technical knowledge of the field require a prominent educational background e.g. engineering, IT etc.