What is the ruling on taking a doubled commission (20 dinars) for a charitable deduction (10 dinars) that a volunteer brings to a charitable committee?

Brokerage is mediating between contracting parties for a fee, and jurists consider it a form of ju'alah (commission). The majority of scholars stipulate that the broker's fee must be known; therefore, it is not permissible for it to be a percentage of the amount transacted, because in that case, it would be ju'alah with an unknown (fee). The proof for this is the Prophet's (peace be upon him) prohibition of hiring a worker until his wage is made clear to him. Some scholars, however, have permitted the fee to be a percentage of the profit, and this view has significant merit. As for profit, there is no limit that is forbidden to exceed, but a Muslim should be generous in his dealings.