Is it permissible to take the amount exceeding 45,0 dinars in exchange for searching for a suitable farm, without the buyer's knowledge?

You are an agent for hire to someone who has appointed you to search for land for his brother. You are not allowed to tell him an unreal price for the purpose of taking a fee or a percentage. Rather, you must state the true price. Your fee must be known at the time of contracting. If you do not agree on a known fee, then you are entitled to a customary fee (ujrat al-mithl).