Increasing the transaction fee for services rendered

Question
If someone asks me to make the effort to finalize some transactions due to the fact that I have knowledge in that particular department, I feel shy to ask for an extra fee in return for my services. Is it permissible for me to increase the basic transaction fee for my efforts without informing the client?
Answer

It is not permissible for you to take anything until you have informed the client and agreed on a price according to the services rendered, as long as you do not work in this department. If, however, you work in that department, any fees taken will be considered a bribe. It is only if you do not work in that particular department, you are allowed to take a fee according to the effort made. The client should not be left to think you are helping him for free while in reality you are taking a fee, so you must inform him beforehand and agree upon a price.