Is there a limit to a commission (جعالة) or brokerage (سمسرة), and is it a condition that the parties to the contract know its percentage?

The basic principle is that there is no limit to the commission except what is agreed upon by both parties. However, Islam calls for leniency in this regard, as the Prophet, peace and blessings be upon him, said: "May Allah have mercy on a man who is lenient when he sells, when he buys, and when he demands his due." It is also necessary that the person from whom the commission is taken is aware of it and consents to it.