Answer:
(Fatwa: 1697/1230/L=1431)
It is the form of brokerage and its fee is lawful provided it is fixed already. Hence, if the commission is fixed and your brother-in-law serves as arbitrator between the buyer and seller, he can do the job of brokerage and can take its fee.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
