Is the commission received from selling gold ounces and the sales policy mentioned in the the company permissible or forbidden in Sharia?

There is no objection to the sales policy adopted by the company, as long as its reality is that the customer promotes a certain amount of its sales. If he sells it, he is entitled to the agreed-upon amount, and if he does not sell, he gets nothing. This falls under the category of 'Ja'l' (stipulated reward), which is permissible and there is a consensus on its general permissibility. The fact that the customer may not be able to sell the entire amount does not prevent the permissibility of this transaction, because 'Ja'ala' allows for a degree of uncertainty and risk that is not permissible in 'Ijarah' (leasing/hiring).