2. (a) Yes, that is the general rule. An agent must have the principal's authority to acquire or dispose of the property in question, otherwise the transaction will not be legally valid. If an agent disposes of the principal's property without authority, the principal may be entitled to recover that property from the third party who has acquired it.

Although this is the general rule, it is subject to some important qualifications.

There are some circumstances in which, even if the agent lacked authority, the principal may not be able to assert their right to property. This is the case where the principal has vested the agent with an apparent right to dispose of the goods, and the third party has relied on that apparent right when acquiring the property, and has given value in exchange for the goods. The relevant doctrine is estoppel.