What is the ruling on trading between a company and customers, where the customer sends their gold to the company in a pouch, then the company estimates the price and sends it to the customer?

The transaction of buying and selling gold and silver via phone and transferring the price through the bank is impermissible due to the delay in receiving both counter-values, which places it under the prohibited riba al-nasi'ah (interest due to delay). It is obligatory for the exchange to take place hand-to-hand in the same session, even if the types differ, in order to avoid riba.