What is the ruling on selling computers in installments, or on commission, or after purchasing the device at the customer's request?

It is permissible to sell computer devices that the seller does not yet own, provided that their specifications are precisely defined and they are easy to obtain, and the full price is paid at the contracting session. This is considered a "Salam sale." However, if their specifications are not precisely defined, or the full price is not paid, or the sale is for specific devices, then it is not permissible, due to the Hadith: "Do not sell what you do not possess." It is permissible to acquire the device first and then sell it, and delaying the payment of its price does not cause harm.