Is it permissible for the main distributor and the sub-distributors to change the prices of the medical products they distribute, whether with or without the knowledge of the business owner, knowing that the main distributor has an agreed-upon percentage, while the sub-distributors change the prices to suit them due to the lack of a direct agreement with the business owner? And is this considered selling what one does not own or a breach of trust?

The mentioned transaction is permissible and falls under the category of lawful brokerage, provided that the owner of the commodity authorizes the increase in price, and that the commodity is sold at its market price, to prevent harm to buyers. It is not a condition for the owner of the commodity to know the exact amount of the increase, based on the owner's statement: "Sell this for such-and-such, and whatever is added is yours." A group of scholars have permitted this, and it is the madhhab (definition) of Ahmad and Ishaq, and it is narrated from Ibn Abbas, who likened it to Mudarabah (definition) (profit-sharing partnership). This is not a case of a person selling what they do not own, as your work and the work of those with you is to guide to the commodity and sell it on behalf of its owner who possesses it, in exchange for the commission you asked about.