A sub-agent is a person employed by and acting under the control of the original agent in the business of the agency (Sec. 190). In simple words, a sub-agent is the agent of the agent. Thus, an agent is the principal of the sub-agent. He really acts in the double capacity. He is an agent of the principal and at the same time, is the principal of the sub-agent.
As a general rule, an agent cannot appoint a sub-agent. However, in the following cases, an agent can appoint a sub-agent:
1. A sub-agent may be appointed if there is a custom of the trade to appoint a sub-agent.
2. Again, a sub-agent may be appointed where the nature of the work is such that a sub-agent is necessary.
3. Where the principal expressly or impliedly allows the appointment of a sub-agent.
4. Where the work to be done is purely ministerial and does not depend upon personal skill, experience, etc. of the agent.
5. Where the principal is aware that the agent will delegate his authority.
6. Where an emergency makes it necessary to appoint a sub-agent.