A sole agency is when the principal is not able to appoint any other commercial agents to act on its behalf in a specified territory (where the sole agent is authorised to act) but the principal is able to seek customers and to negotiate sales directly for itself.
An exclusive agency is when the agent has the exclusive right to represent the principal in a territory and the principal is prohibited from trying to seek customers and to negotiate sales directly for itself.
A non-exclusive agency is when the principal is free to appoint other commercial agents in the same territory and also, seek customers and sales/transactions itself.