Is it permissible to take an additional amount on top of the price of a commodity set by the company as a result of convincing the customer, knowing that this amount is taken for oneself?

You are an agent for the company in selling its products, and you must adhere to the limits of the agency. It is not permissible to increase the price set by the company. What you took for yourself without the company's knowledge must be returned to it or you must seek its halal (permissibility) for it.