Is the percentage taken by the intermediary for reconciling between painters and customers permissible or impermissible?

There is no harm in guiding customers to craftsmen in exchange for money you take from the craftsman for each customer who comes to him through you, whether it is a fixed amount or a percentage. This is called the broker's and guide's fee. It is permissible for the guide to take a known percentage of the price at which the commodity settles, in exchange for guiding to it, and he collects it from the seller or the buyer according to the agreement, without injustice or harm.