Is it permissible for a merchant to take an additional sum for delaying payment until the time of receiving the goods in an online purchase transaction?

Delaying payment when purchasing goods online can occur as follows:

1. Specific good: Payment for a specific good may be delayed, and the buyer has the option upon seeing it. It is permissible for the deferred price to be higher than the spot price, provided that one of them is agreed upon at the time of the contract. 2. Good described but not specific (dhimma): The full price must be paid at the contracting session, and delaying payment is not permissible, because this sale is a salam (forward) sale. 3. Described good with cash on delivery (COD): This is permissible if the sale takes place upon receipt and inspection of the good. What precedes this is considered a promise to purchase. It is not permissible to complete the sale before the good arrives and payment is made, because it falls under the category of selling debt for debt (al-kali' bi al-kali').

Based on this, increasing the price in exchange for delay is not permissible except in the case of selling a specific good, with agreement on one of the two prices (spot or deferred).