Are the sums of money saved by a person from gratuities that he used to pay to get his work done, and which he now performs himself with great effort, halal or haram?

If you are an agent and pay gratuities from your principal's money to finalize tasks, then either this payment is for a service that neither you nor the worker performing it is obliged to do, in which case it is permissible if your principal explicitly or customarily authorizes it. However, if the work is obligatory for you, then it is not permissible to pay without your principal's permission. And if it is obligatory for the worker, then the payment is a prohibited bribe, unless it becomes the only means to obtain a right, in which case the sin is upon the recipient. And taking an amount for yourself from these gratuities is not permissible without your principal's knowledge, because an agent is entrusted and acts only with the permission of their principal.