What is the ruling on the money taken by a broker if he raises the price of goods for the buyer without the buyer's knowledge of the original prices?

The agent is trustworthy concerning what he has been entrusted with, so it is not permissible for him to betray the trust by lying about the price of the goods and taking them at a price higher than their real value. However, he can agree with his principal to take a sum in return for his efforts, or a brokerage fee. If they agree on that, then there is no blame upon him. But without an agreement, it is not permissible for him to take anything except with the knowledge and permission of his principal.