What is the ruling on brokerage, which involves mediating between the seller and the buyer to facilitate a sale, and is it permissible or impermissible (halal or haram)?

There is no harm in brokerage if the Sharia's regulations are adhered to, such as the clarity of the fee and the work, and the permissibility of the commodity. As for the tree marketing on the aforementioned website, it is not possible to rule on it without examining its true nature.