Is it required that the commission or fee charged by an intermediary be known to the client, in the event that the intermediary manages and delivers a service contracted with a third party?

If a person agrees with a client to perform a service for a known fee, and the client does not stipulate that the work must be done by the person themselves, then there is no harm in subcontracting the work to another for a lower fee. There is no need to inform the client about the difference in fees. The proof for this is: "If one undertakes a work for a fee — such as tailoring or other services — it is permissible for another to undertake it for less."