Is it permissible for me to increase the price of the apartment agreed upon between me and my partner, should I mediate its sale to my friend, and consider this increase a commission?

The issue can be summarized in two scenarios:

1. If the agent sells the property for a price higher than what was specified, the increase belongs to the owner, and the broker is entitled only to his commission. The owner may give him the increase as a commission. 2. If the owner says to the agent: "Sell for such-and-such a price, and whatever exceeds that is yours," scholars have differed on the validity of this contract. The preponderant opinion, which is the view of Ibn Abbas and Imam Ahmad, considers the contract valid and the agent entitled to the increase. This is based on the companions not opposing Ibn Abbas and the permissibility of contracts unless they involve usury (riba) or excessive uncertainty (gharar). Others, however, consider the contract void and that the agent is only entitled to a fair wage (ujrat al-mithl).