Does the car remain the property of the seller, or does its ownership transfer to the buyer upon mere agreement and before delivery? And when does ownership transfer to the buyer? And is the seller's money considered unlawful (haram) if he sells the car to someone other than the first buyer before delivering it to him?

If a valid sale contract is concluded with offer and acceptance, ownership of the sold item transfers to the buyer immediately upon the contract, even if the exchange of possession has not occurred.

Accordingly, if someone sells a car to one person and then sells it to another, the second sale is invalid because he sold what he did not own.

However, if the seller and buyer agree on a sale but the contract is not concluded, and then another buyer comes and offers more, and the seller sells it to him, this sale is forbidden but valid, and the price is not forbidden, but the seller is sinful.