When can an agency be not revoked?

An agency is irrevocable in the following cases:

Where the agency is coupled with interest [Section 202]. Where the agent has himself an interest in the subject matter of agency, the agency is said to be coupled with interest. Such an agency is created with the object of protecting or securing any interest of the agent. So where a creditor is employed for valuable consideration as an agent to collect moneys from third parties and pay himself the debt due to the principal debtor, the principal thereby confers an interest on the agent and authority cannot be revoked unilaterally during the subsistence of the interest in the absence of an expressed contract to the contrary. Even the death or insanity of the principal does not terminate the authority in this case.

Where an agent has incurred personal liability, the agency becomes irrevocable, for the principal cannot be permitted to withdraw, leaving the agent exposed to risk or liability he has incurred.

When the authority has been partly exercised by the agent, it becomes irrevocable in particular with regard to obligations which
arise from acts already done [Section 204].