Praise be to Allah.
There is nothing wrong with the process mentioned; it is very similar to the permissible type of brokerage, on condition that the company owner gives permission for the increase in price and that the product is sold for a price similar to the market price, so as to avoid causing harm to the purchasers.
It is only stipulated that the company owner should give permission for the increase in the price because the broker is in a position of trust, and whatever profits he makes should go back to his employer. He does not have the right to take the extra amount without permission.
It is not stipulated that the company owner should know the amount of the increase. So he may say: “Sell it for ten, and anything more than that is yours.”
If the owner says, “Sell it for such and such, and anything more than that is yours,” this is something that was allowed by some scholars, as is the view of Ahmad and Ishaaq (may Allah have mercy on them), and was narrated from Ibn ‘Abbaas (may Allah be pleased with him). They regarded this as being akin to mudaarabah (where investors provide capital and others supply their expertise and effort, and the profits are shared between them).
Al-Bukhaari (may Allah have mercy on him) said in his Saheeh:
Chapter on the fee of a broker: Ibn Sireen, ‘Ata’, Ibraaheem and al-Hasan did not see anything wrong with the fee of a broker. Ibn ‘Abbaas said: There is nothing wrong with saying, “Sell this garment and anything more than such and such is yours.” Ibn Sireen said: “If he says, ‘Sell this and whatever profit you make is yours, or will be shared between you and me,’ there is nothing wrong with that.” The Prophet (blessings and peace of Allah be upon him) said: “The Muslims are bound by the conditions.” End quote.
Ibn Qudaamah (may Allah have mercy on him) said in al-Mughni (5/86):
If he says, “Sell this garment for ten, and anything more than that is yours,” that is valid and he is entitled to the extra amount. But ash-Shaafa‘i said: It is not valid; however, we may note that Ibn ‘Abbaas did not see anything wrong with that, and because he is disposing of his property with his permission. This is like the case of mudaarabah and musaaqaah (when trees are given to someone to tend and irrigate in return for a share of the harvest). End quote.
This does not come under the heading of selling that which one does not possess, because your work and that of those who work with you is telling people about the product and selling it on behalf of its owner who does possess it, in return for the commission you asked about.
You are not selling an item that you bought but did not take possession of, and you are not selling on your own account; rather you are selling an item that belongs to someone else as an agent; the broker is an agent working for a fee and is not buying from the owner.
And Allah knows best.