What is the ruling on agreeing with the landlord to conclude a lease contract without the knowledge of the broker, and not giving him his commission, under the pretext that his commission is excessive?

If it is customary in your country that the work of a broker is completed merely by pointing out a house, even if the contract is not finalized through him, then he is entitled to the agreed-upon fee. If such a custom does not exist, then his pointing out is considered a commencement of work, and as long as the abandonment is from your side, he deserves the fair market value for the benefit and effort he provided.