The fees of brokering are estimated according to `Urf (custom) in defining its amount and who should pay it and to whom. If the two sides agree and consent of what is not the custom, there would be nothing wrong with that. But if they do not know the percentage or they do not agree on that percentage, it is not permissible. This is because the money of any Muslim is not permissible to be taken except with his consent and free will according to the abundant evidence in the Qur'an and Sunnah (whatever is reported from the Prophet).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.