What is the ruling on selling a car if the seller has increased its price at the request of an intermediary to obtain a commission from the buyer?

Brokerage is permissible. It involves searching for a buyer for a seller's goods, or searching for a seller for a buyer's need, and mediating between them to facilitate the sale process. What your friend did in this regard is permissible, as long as the sale was concluded with the buyer's consent, there was no significant deception, and the car did not have a defect that was concealed from him. This is because a sale conducted in this manner involves no deception, no fraud, no ambiguity, and no undue risk. Therefore, it remains permissible based on its fundamental permissibility, as Allah Almighty says: ﴿But Allah has permitted trade﴾ [Al-Baqarah:275].