What is the ruling on working in a store that sells on installment, where the store takes a security deposit from the customer, then buys the commodity for him, and deals with the bank which pays the price of the commodity to the store in cash and collects its installments from the customer, noting that the store sells the commodity for almost double its price?

Selling on installment for a price higher than the cash price is permissible, and buying an item for a customer and then selling it to him on installment is permissible. As for the involvement of a bank: if the bank genuinely buys the item and then sells it to the customer on installment, there is no harm. However, if its role is merely financial, by paying the amount to the customer and recovering it with an increase, then this is usury (riba). A company that acts as an intermediary between a usurer and his client is considered an accomplice in sin, and cooperation in sin and aggression has been forbidden. Furthermore, taking a post-dated check from a customer and then discounting it at the bank for a cash value is considered usury. The correct scenario is to sell the item directly to the customer and allow him to pay the price in installments, with the possibility of taking a guarantor to secure the right.