What is the Islamic legal ruling on the transactions followed by the exhibition organizing company, which arranges with an Islamic bank to organize an exhibition for selling goods in installments to company employees, whereby the company is authorized to buy and sell on behalf of the bank, and the installment is calculated based on the purchase price plus the profit of both the company and the bank? Employees choose the goods and register their preferences without being obligated to purchase. Then, the goods are bought from suppliers and delivered to customers, and the suppliers' dues and the company's commission are disbursed by the bank, with the possibility of returning unsold goods and a special installment system for those who wish to pay a cash down payment, noting that the bank does not charge late payment penalties? And what is the legitimate condition that can be added to the contract to compensate for late payment?

The bank's authorization for you to buy, sell, and organize the exhibition on its behalf falls under the category of brokerage (simsarah), which is permissible in Islamic law, as long as it does not involve assisting in the sale of something prohibited. This is considered by jurists as a form of ju'alah (a contract for a specified reward for performing a task). However, the supplier's action of bringing the requested goods to the exhibition, delivering them to the customer, and accepting the return of any remaining items indicates that these sales were not under the bank's guarantee before being sold to the customer. This is impermissible, due to the Prophet's (peace be upon him) saying: "It is not lawful to combine a loan and a sale, nor two conditions in one sale, nor profit from something not in your guarantee, nor selling what you do not possess." As for the penalty clause for compensating late payment, it is pure usury (riba) and forbidden. The permissible alternative is for the buyer to provide a collateral (rahn) that grants the creditor the right to collect his debt if the debtor delays payment.