A condition of selling gold for gold is equality and immediate exchange

Question: I have some old jewelry. I went to the market to sell it and offered it to one of the merchants. He took it and gave me other jewelry in exchange, without taking any extra from me or giving me any extra. I thought that this was not permissible, so he told me that the weight of what he took from me and what he gave me was equal, and I believed him in that.
I ask for your ruling on this transaction, knowing that I cannot return the gold to him now if the transaction is not permissible.

Answer: If they were equal in weight and exchanged in the same session, there is no harm in that. And if one of them was of better quality than the other, that is due to the generality of the authentic hadiths on this matter. And if he was lying, the sin is upon him.