Putnam's Handy Law Book for the Layman

A particular usage or custom also affects an agent's powers. If the principal confers on him authority to transact business of a well-defined nature, bounded by well-defined usage and customs, the law presumes the agency was created with reference to them. This protection affects agents and third persons alike, the latter therefore who act in good faith in such dealings are protected against secret limitations of which they had no notice.

An agent has no authority to purchase his principal's property. To do this, in a sense, would be to purchase of himself. The temptation to do this is sometimes very great, too great for him to withstand, and so he resorts to a crooked method for accomplishing his end. He