Is it a condition in a forward sale (bayʿ al-salam) that the price be paid at the time of the contract? And does this condition cease to apply if the intermediary website transfers the price to the seller within a week, with the seller knowing that he does not possess the commodity before the money arrives? And is it permissible for the buyer to return the goods and receive his money back if he does not like them?

A Salam transaction is the sale of a described item to be delivered in the future for an upfront payment received at the contract session. For its validity, the majority of scholars stipulate the full payment of the capital at the contract session. This is derived by Imam Al-Shafi'i from the Prophet's (peace be upon him) saying: "Whoever pays in advance for dates, let him pay in advance for a known measure and a known weight, until a known term," and to avoid it being a sale of debt for debt. The Malikis, however, dissented, permitting a delay of two or three days for the capital payment.

If the buyer pays part of the price and delays the rest, the Salam contract becomes void for the unpaid portion.

As for the intermediary website, if it acts as an agent for the sale and receives the payment, its receipt is valid. If you authorize it to conduct the contract and receive the full payment, the Salam contract is valid, and the agent's delay in transferring the money to you does not harm the contract, provided that the money is in its possession as your property and under your guarantee.

It is not a condition in Salam that the buyer knows whether you own the commodity or not.

You are permitted to allow the buyer to return the commodity even if its description matches and it is free of defects, whether this is due to a pre-stipulated condition (Khiyar al-Shart - option of condition) or as a recommended rescission (Iqalah).