What is the ruling on buying a car in installments from German car companies, given that there is no third party in the sale process, as each company owns its own bank through which the sale is conducted?

If the purchase is from a bank, the bank must first own the car, and then sell it in installments; otherwise, it is an interest-based loan.

As for purchasing directly from the company, there is no harm in it, even if the installment price is higher.

However, if the bank intervenes in the transaction to pay the full amount to the company and then recovers it from you in installments, this is usury (riba).