Is it permissible to deal with a merchant who determines the price of goods based on the buyer's desire and specifications, then adds his profit to it, and then gives the buyer the choice between immediate payment at a certain price or deferred payment at a higher price and in monthly installments, with no penalty clauses for late payment?

We understand that a merchant procures goods based on customers' promises to buy, then concludes the sale contract with them after the goods arrive and the price is determined. There is no harm in this, and it is permissible to deal in this manner.

However, giving the buyer a choice between two prices—one deferred and one immediate—in a single contract is not permissible, because it falls under the category of "two sales in one."

But if the choice occurs during negotiation, and the contract is not concluded except at a specific price, whether deferred or immediate, then there is no harm in this according to the majority of scholars, even if the deferred price is higher than the immediate price, because deferment has a share in the price.

It must be noted that it is not permissible to conclude a sales contract until the merchant owns the goods, unless the contract is a salam contract with its conditions.