Is it permissible to buy a plot of land that a son is selling without the knowledge of his wealthy father, and is it permissible for me to mediate in this transaction for a commission?

It is not permissible for a person to sell what he does not own, and this is a matter of consensus among scholars.

Accordingly, it is not permissible for the son to sell plots of land owned by his father except with his father's permission. His justification that his siblings do so, or his intention to deduct the price from his gift or inheritance, is not valid, as this is a form of deception and unlawfully consuming people's wealth.

Likewise, it is not permissible to mediate in the son's sale of these plots because it constitutes cooperation in sin.