What is the ruling on installments that accrue to the questioner and his partners from the sale of a car by installments, which was carried out with a suspicion of the invalidity of the sale at the time, and does the sin of this sale fall on the one who carried it out or on everyone?

The delivery of goods from the first seller's store does not affect the validity of the installment sale. It is sufficient for the second seller to receive them and for them to enter into his possession before he sells them. There is no harm in agreeing on the deferred price for the second sale before the completion of the first sale, as this falls under the category of non-binding promise and negotiation. Once the second seller takes possession of the goods after the first sale, the binding contract for the second sale is concluded. Based on this, there is nothing that invalidates the contract or makes the profit unlawful.