What is the ruling on taking a commission when mediating between a buyer and a seller? Is it obligatory to inform the client if the commission is taken from the producing company? Is it permissible to pay a portion of the merchandise's price on behalf of a buyer who is late in payment, on the condition that the merchandise becomes my property and I sell it to him at a price I deem appropriate?

It is permissible to take a commission for brokerage (mediation between a seller and a buyer) unless it involves a prohibited sale. It is permissible to take it from one party or both, according to custom or agreement. There is no objection to not informing the buyer of it if it comes only from the seller or the producing company, and there is no deception involved. If you pay part of the price of the goods due to the buyer's delay in payment and you are a guarantor for him, then you are a lender to him for that amount, because the goods become the property of the buyer upon contract. It must be noted that it is not permissible for the producing company to give you a commission in return for guaranteeing the buyer, as this is a benefit in exchange for a guarantee, which is forbidden by Sharia.