What is the ruling on purchasing a taxi in installments with an increase in price, and is this considered usury (riba)? And what should the buyer do about it?

If the sale was based on a promise, and then the merchant bought the car and it truly entered his possession, and then he sold it to the man, the sale is valid because it is a Murabaha sale. However, if the sales contract was concluded before the merchant bought the car, the sale is invalid because he sold what he did not own, and this is unanimously prohibited. Consequently, the buyer must return the car to the seller, unless its market value has changed, in which case it is valued according to the day he took possession of it, and its yield belongs to the buyer.