An estate agent is often employed by a principal, for example, to find a buyer for the principal's property. The extent and duration of the estate agent's power to represent the principal will depend on their particular agreement.
Travel agents, though described as 'agents', are not always true agents, because they may not have any power to represent a principal. Very often, a travel agent is only acting as a channel of communication, to facilitate a transaction that is then entered into directly by the relevant parties. But it is not impossible for a travel agent to be given agency powers in particular cases.