Is brokerage in buying and selling permissible or forbidden, and what is the permissible percentage of profit from the capital?

Brokerage is permissible, as long as it does not involve aiding in a forbidden sale, and it is considered a form of ju'l (commissions/fees). There is no specific limit to the percentage of profit, according to the preponderant opinion of scholars. A Muslim merchant should not be greedy or selfish; rather, he should observe the ethical aspect in his dealings, as the Prophet, peace and blessings be upon him, said: "May Allah have mercy upon a man who is lenient when he sells, when he buys, and when he demands his rights."