What is the ruling on banks dealing in the sale of goods, houses, and cars through Murabaha (cost-plus financing), and what is the ruling on the bank taking a service fee, and signing deeds where the amount is not written, and the bank specifying certain places for purchase, and what is the ruling on buying goods in installments from stores?

The scenario mentioned is correct, and there is no impediment for the bank to impose a fixed amount on the customer, which it calls a service fee. This amount is included in the price and is known at the time of the sale contract. The important thing is that the bank genuinely purchases the goods before selling them to the customer. There is no harm in increasing their price above their purchase price, and there is no harm in purchasing in installments from stores, provided it adheres to Sharia guidelines.