It is the duty of the broker to act in the best interests of his employer and to obtain the best price and terms for him. He is bound not only to good faith but to reasonable diligence, and to such skill as is ordinarily possessed by persons of common capacity engaged in the same business. He must follow instructions and not exceed his authority. He must reveal to his principal all information that may come to him relating to the transaction under consideration. Concealing facts material to the interests of his employer amounts to fraud. The broker may, for example, know that a prospective purchaser has actual need of his employer's property. He should advise his employer of this in order that the owner may get a better price or that he may not be moved by arguments to accept a lower price. The broker however is not obliged to violate a confidence. If he knows that a prospective purchaser is not acting for himself but for some one else and he is in honor bound not to reveal the fact, he may withhold it but he should apprise his employer that he is dealing with an undisclosed principal.