What is the ruling on authorizing the client who is obligated to sell the car after acquiring ownership of it from the installment sale institution, and what is the ruling on stipulating a sum of money as administrative fees or office charges upon signing the contract, knowing that the commodity is owned by the institution?

If the customs card accurately describes the car, then taking possession of the card is considered taking possession of the car, because vacating the premises (takhliyah) is a legitimate form of possession. The Hanafis consider takhliyah (removing obstacles and enabling possession) to be constructive possession.

Based on this, there is no objection to selling the car using the customs card, even if the buyer commissions the showroom to sell it on their behalf, unless there is an agreement for the car to return to its original seller.

As for stipulating administrative fees, there is no objection to them if the buyer is aware and consents, as long as there is no deception or fraud involved. It is preferable for these fees to be added to the total price of the car, as everything stipulated by the seller is considered part of the sale price.