What is the ruling on purchasing an agency from a company for a single product, whereby the buyer becomes an agent and is entitled to market the company's products in exchange for a commission on sales, and is not required to purchase other products, and this agency differs from traditional agencies that require paying exorbitant amounts just to obtain the agency document?

If your work is limited to selling permissible goods of the company in exchange for a commission or a percentage of the profits, and you have no relation to the goods after their sale, and you do not receive a commission on subsequent sales merely for having guided the first buyer (which is known as prohibited pyramid marketing), then there is no harm in your work. This falls under permissible brokerage and ju'ala (commission for a specific task). Nor is there any harm in the company stipulating the purchase of one of its products to obtain an agency contract.