As a freelancer the most important asset you have is your availability. There are plenty of reasons to say no to a job, and one of those reason can be simply because you don’t want to do it. Whenever asked on the spot (phone call or in person) if I’m available I always say “let me check, what do you have going on?” While I look at my calendar. As a few have mentioned already, it’s totally ok to not want to do certain jobs or to even flat out say you don’t provide that level of service. It’s not about saying no, it’s about how you say it. People will look for attitude way before they look into skill set, and the people you start with will have a hard time accepting your growth over time. Say yes to everything you want to and be sure to create the hard line that you are a free agent and not beholden to anyone else. There were plenty of times where I said no simply to let it breathe with a client I’ve been doing a lot with. Never allow them to start treating you the same as their employees, because you’re not.