What is the ruling on trading with installment payments using money if there is a fear that the agent might sell fictitiously without actually possessing the car, in order to avoid usury and prohibited transactions?

If you suspect that the showroom owner deals in unlawful matters, you must verify it. If it becomes clear to you that he is innocent, then there is no harm in dealing with him. Otherwise, it is not permissible, because it constitutes cooperation in sin and aggression, and his earnings are illicit.

The described form of sale is prohibited for two reasons: 1. Bay’ al-’Inah ( ’Inah transaction): “If you engage in ’Inah transactions, and grasp the tails of cows, and become content with cultivation, and abandon Jihad, Allah will inflict upon you humiliation which He will not remove until you return to your religion.” 2. Selling what you do not possess: “Do not sell what you do not have.”