What is the ruling on taking commission from the seller or the buyer, and what is the ruling on taking it without their knowledge, and what is its permissible percentage if it is allowed?

Brokerage is permissible, and it is permissible for the broker to take their fee from one party or both parties, according to the agreement, provided that the party from whom the fee is taken is aware. Otherwise, it would be consuming wealth falsely, based on the Almighty's saying: "And do not consume your properties among yourselves falsely." Awareness is stipulated because brokerage is a ju'alah (a contract for a reward for a specific task) that requires offer and acceptance. As for the broker taking a commission from the seller without the buyer's knowledge, and vice versa, there is no harm in it. The amount of the fee is determined by agreement.