SHAFAQNA – The Grand Ayatollah Makarem answered a question about middleman’s profit.
Question: What is the ruling on the profit of the middleman who sells others goods?
The Grand Ayatollah Makarem: When an item is given to a person to sell for a specific price and that person is told that the added amount on top of the sale price belongs to him, the deal is correct, and the added amount belongs to the middleman. Also if it is said that I sold you this item with this price and the person accepts it, the extra amount that item is sold for; belongs to that person.
Source: PERSIAN SHAFAQNA