What is the ruling on taking a commission from manufacturing companies in exchange for researching and corresponding on their behalf with a merchant, while also taking a fee for time from the merchant himself, given that the merchant is unaware of the commission the intermediary receives, and that this commission is sometimes added to the price of the commodity, thereby increasing the price for the merchant?

Brokerage and commercial mediation are legitimate and permissible, and the broker's fee is considered either a ju'ala (reward for a specific task) or ijara (lease/hire). It is permissible for the agreement on the mediation fee to be estimated based on the transaction or the time spent. The role of the mediator is limited to bringing the contracting parties closer together, and they do not undertake the execution of the contract unless authorized to do so. The fee can be a lump sum or a percentage, and it becomes due upon completion of the work or expiration of the agreed-upon period. A broker may take commission from both the seller and the buyer simultaneously if there is an agreement or if custom dictates it, and it is not a condition that each party be aware of your agreement with the other party. If you are an employee with a monthly salary at a marketing company, you are not permitted to take an additional commission unless the company allows it, for example, by setting a price for you and saying: "If you sell for more, it is yours."