What should a gold shop owner do with the amount of money received for gold that the buyer did not collect due to not bringing identification?

The sale of gold for cash requires immediate possession (taqabud) at the time of the contract. It is not permissible to sell it on installments or with a deferred payment. Purchasing with a credit card (Visa) is often a deferred sale because the seller does not receive the payment immediately, and this is not permissible. However, if the payment reaches the seller's account immediately and at once, then the sale is permissible. In the impermissible case, the amount withdrawn is a trust with the seller, and the questioner must repent. In the permissible case, the gold is a trust with the seller until the buyer takes possession of it.