Question: If a man says to another: “Find me a buyer for my car and you will have such-and-such if the sale goes through,” or says: “Find me a car of such-and-such and bring me together with its owner, and you will have such-and-such,”—is it permissible for the intermediary between the two parties to take that money?
Answer: What appears to me is that it is permissible for the intermediary between seller and buyer to take what is stipulated for him, because he takes it in exchange for a service and work for the seller or the buyer, or for both, with the giver’s willing consent.
However, the intermediary must avoid in his mediation and brokering lies, deceit, stratagems, and trickery; for that is impermissible.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2