Good luck and how did it go?As roger says it's for a charity. I agree fully, that is why you have to say no to certain work. I have done this for free but have work now lined up for 3 more jobs with the agency all paid. I guess it is a sort of test run for the standard of my work, while getting me enough experience.
Got to start somewhere and unfortunatley with that many people offering the same service got to do the free jobs to get anywhere. Same as working as a runner for nothing on TV/film work