A:
It is not permissible to sell cars, whether by cash or credit, by installments or not, until the ownership of the cars has been transferred to the new owner, and they have full possession of them. The first buyer should receive the cars, fully possess them, and transfer them into their ownership.
Getting the customs documents before possession and full ownership is not considered as acquisition or receipt. Therefore, selling a car based on the customs documents, before receipt and full possession, is considered to be an invalid sale. It is Haram (prohibited) to deal in this way, and it is obligatory that any sales conducted in this manner should be voided and any money paid should be returned to the payer. It is not Halal (lawful) to take money for these cars without a new contract being made after (Part No. 13; Page No. 258) the ownership of the car is transferred to the new buyer and they have full possession of it.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.