Is it permissible to withdraw from a verbal promise to sell after a long wait and an increase in the property's price? Is it permissible to compensate the other party for this wait, or is that considered usury (riba)? And is it possible to renew the sale in writing at prices consistent with the current situation?

First: If the sale was concluded and the seller refused to hand over the house, the sale is valid, and the house legally belongs to the buyer, whether the buyer paid the remaining price or not.

Second: Details regarding what the buyer's relative paid as a down payment: 1. If it was merely a promise to sell, it is not considered a down payment (ʿurbūn) in Islamic law, and the owner of the house must return the money. 2. If it was a definitive sale, the more probable opinion is that it is an invalid sale, based on the Prophet's (peace be upon him) saying: "Do not sell what you do not possess," and based on the statement of Sheikh Ibn Baz, may Allah have mercy on him: "It is not permissible for a Muslim to sell an item for cash or on credit unless he owns it and has taken possession of it." Possession of real estate is achieved by handing it over to the buyer and enabling him to dispose of it. Since the sale was concluded based on the belief in its validity, and the second buyer paid a portion of the price, justice necessitates that the last buyer owns a share in the house proportionate to what he paid of its price. They can either agree to be partners in it, or sell it, or the second buyer can complete its price at its current market value, or they can annul the sale based on what they agree upon.