What is the ruling on a goldsmith including the weight of the iron present in the lock of a gold necklace in its price during buying and selling?

There is no objection to buying and selling gold for money by selling the gram of iron contained in a gold necklace at the price of gold, and buying the gram of iron at a price lower than the price of gold. The transactor has the right to accept or reject this, as Allah Almighty says: ﴿O you who have believed, do not consume your properties among yourselves through falsehood, but [instead] let there be a trade [involving mutual] consent among you.﴾