I have never charged a friend for a service that I performed for them that is within my professional area of expertise or ability to help them out. I have helped them to write speeches for simchas, to write grahmin, to chauffeur around their kids when they were working and unavailable to do their carpool, to take their parents to doctor appointments, etc. If you are a friend, you do these things out of love and chessed.
That said, if they were just casual acquaintances, I might charge them much less than I would a fremdeh, but I would still want to be paid for my work.