What is the ruling on marketing goods at a price higher than their owner's price, and paying the owner's due after the sale, while taking the difference as profit?

The described scenario falls under selling what one does not own, which is prohibited in Islamic law, due to the Prophet's (peace and blessings be upon him) saying to Hakim bin Hizam: "Do not sell what you do not possess." The permissible alternative is for you to act as a broker for the owner of the goods for a known fee, or for him to agree with you that whatever exceeds a certain price is yours.