Is it permissible to authorize someone from a jewelry store outside the city to receive and pay the amount for the gold and ship it?

The simultaneous exchange (hand-to-hand transaction) in the same session is a condition for purchasing gold with money, based on the hadith (definition) of 'Ubadah ibn al-Samit: "Gold for gold... hand to hand." Monetary currencies take the same ruling as gold and silver. If you do not receive the gold yourself, then appoint someone other than the seller or his agent to receive the gold and pay the price; this fulfills the condition of simultaneous exchange in the same session. It is not permissible to retain the value of old gold for the purpose of purchasing new gold from the same seller.