This is something I’ve only recently started doing, saying no to jobs because they don’t fit either my schedule or my niche.
But I’ve learned the hard way. I would never say no to any work. I think it’s something ingrained from being completely broke financially, you never want to go back to that so you’re afraid to turn anything down.

Unfortunately running your business like that is actually counterproductive and can affect your income negatively even if you don’t realize it.
In my case, I would have so much going on at once; parts on order from different places, information coming in from all directions, while still trying to keep up with the daily work that paid the overhead. Basically, I was trying to juggle too many things at once. And I was never one to ask for help.
But learning to say no in certain situations has brought me a much calmer environment. And best of all, my earnings are good, steady, and more predictable. I still take on odd or awkward jobs – that’s something I specialize in – but I don’t overload myself.
It wasn’t easy to start saying no. It went against every instinct I had. But so far it’s working. A change of environment and a change of pace can really be a good thing.