What is the ruling on taking a 10% commission from the buyer in exchange for mediating between him and the seller of a rikaz (treasure), knowing that this percentage must be concealed from the seller because the rikaz belongs to orphans?

If not informing the seller about your agreement with the buyer is not considered fraud or deception, then you are not obliged to inform him.

If the percentage is a donation from the merchant, then it is a permissible gift.

However, if the percentage is based on a prior agreement, then it is permissible to agree upon a known commission for your guidance to the seller, and ten percent is considered a known commission if the price of the commodity is known.

If the price is unknown at the time of the brokerage contract, then the commission is unknown and is not valid according to the majority of scholars, while a group permitted the commission to be a percentage of an unknown profit.