What is the ruling on buying a taxi by installments through a bank, where the bank buys and owns the car, then sells it to me at a higher price on an installment basis?

There is no objection to the bank first purchasing the car for itself, and then selling it to you in installments for a price higher than what it paid for it, as installment sales include a share of the price. There is also no objection to the bank stipulating certain guarantees to enter into the transaction, such as obtaining a third-party guarantee, or mortgaging the customer's deposit, or mortgaging any movable or immovable property, or mortgaging the commodity subject of the contract.