There are two strong opinions on this and freelancers are usually firmly in one camp or the other. Some believe free work is a fair trade early on because it gives you real samples to show paying clients. Others feel it sets a bad tone and teaches clients to undervalue your work from the start. The answer probably depends on where you are in your career and what you are trying to build. Did you do free work when you started and do you think it helped or hurt you in the long run?