Is it permissible to deal with an iron merchant who cancels a previous booking at its price and makes a new booking at two different prices or at a single price, depending on the fluctuation of the iron market price, whether rising or falling?

If the amounts are paid to demonstrate seriousness in the intention to purchase and as a promise, and then the contract is concluded upon receiving the iron, there is no harm in that. However, if it is in the form of concluding a binding contract, then the iron must be present with the merchant at the time of the contract. The transaction can be corrected by the buyer placing his money with the merchant and appointing him as an agent to purchase the iron for him according to its price at the time of purchase, with a fee calculated for the merchant if he does not offer it as a gift.