Is it impermissible to sell a specific commodity to a private company in exchange for pre-agreed percentages that vary according to the activity and the extent of promoting the commodity and gaining more customers (what is called "marketing")?

It is permissible to promote a company and sell its goods for a specific percentage of the price that increases with the increase in sales. This transaction is considered brokerage (samsara) and is Islamically permissible (ja'iz sharan). It falls under the category of ju'ala (reward for a service), as in the Almighty's saying: "And for he who brings it is a camel's load, and I am responsible for it." For this to be permissible, the goods must be Islamically permissible; otherwise, promoting them would be forbidden, due to the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." As for pyramid marketing, it is forbidden due to the gharar (excessive uncertainty) and gambling involved in it.