What is the ruling on taking a percentage of the money agreed upon between the client and the workers, and to what extent does this affect the issue of deception?

Your agreement with the client to bring workers is a brokerage contract. It is permissible for a broker to take a commission from one party or from both parties, according to the agreement. It is also permissible to take it from one of them without the knowledge of the other. What is forbidden is taking a commission without the knowledge of the one from whom it is taken. If the wage agreement between the workers and the client is without your intervention, then there is no harm in you taking a commission from the workers in addition to what you take from the client, whether the client knows about it or not. It is preferable that your commission be a fixed amount.