To what extent is the action of the intermediary who bought a feddan of land from the young man's mother for a pittance and sold it for ten times the price legitimate, and is the young man entitled to recourse against him to reclaim his right?

If the intermediary deceived the mother in the sale, then the sale falls under the ruling of a sale to a mustarsil, who is someone ignorant of the value of the commodity. The majority of jurists have held that the option [to revoke the contract] is established due to ghabn (gross deception/discrepancy) if one party to the contract deceives the other. It is best to present this issue to the people of knowledge in your country.