If you did it once and it didn't feel good or work out how you wanted, does that mean you'd be a fool to do it again?
Do you have a clear understanding of why you're doing it? What story is it telling in your life? What larger narrative is that enabling? What narrative(s) does it allow you to let go of? Are you able to identify which parts of the job for which you're not only qualified, but are also willing and able to do in a way that is sustainable and generative for all parties involved? Do you have a clear understanding for what sustainable and generative mean for this work? What is the container for the work? Timeline? Weekly time expectation? Communication strategies? What do you need in the rest of your environment to support the work? What level of compensation do you need to feel valued in the work? What if some of your above needs aren't met?
The answer to all of these questions are the stones that create boundaries. The goal of good boundaries aren't to keep things away, but to create entryways through which only the things that we wish to allow into our live can pass.
The answer is usually never no, it's maybe if. More importantly, it's here is what I need. When I set boundaries, I respect your agency to allow you to set your's. That's when negotiation begins.