Selling gold for silver without exchanging them in the same meeting

Q 2: Is it permissible to calculate the value of gold in cash if a friend of ours happens to buy gold at our shop without paying the price? Should we consider it a form of loan? Is it also permissible, for example, that when he buys gold for 4850 riyals, we give him 150 riyals so that the total is 5000 riyals as a loan or pay him the 5000 riyals in cash as a form of loan? Please, what is the ruling on that?

If the case is as you mentioned, it is prohibited because this involves exchanging gold for silver or what takes its ruling, without conducting the transaction hand-to-hand.