Is the described method of selling—where goods are displayed before being acquired, an agreement is made with the client, then the goods are bought and sold, sometimes with a deposit taken—considered a supply contract (عقد توريد) or a forward sale contract (عقد سلم), and what is its ruling?

If the customer is aware that the goods are not available and will be provided later according to his desire, and then the sale contract is concluded after they become available, this is a normal sale and not a salam sale. It is permissible to request a sum of money from the orderer to guarantee his seriousness, and in case of his reneging and the seller being harmed, the seller may take a portion of the down payment equivalent to the actual damage incurred. The most important thing is that the sale contract between the seller and the customer should not be concluded before the seller purchases and possesses the goods; based on Ibn Qudamah's statement: "It is not permissible to sell an item one does not own." As for a salam sale, it is a contract for something described in the debtor's liability with precise specifications, to be delivered to the buyer at a known future date, and it is a condition that the capital be paid in full at the time of the contract.