Besides familly I only have 5 people in my life that my answer is always yes when they ask if I can do something for them. Anyone else I will ask a few questions and set some rules before I do a favor for them. Cheers!
But, after reading others' answers, and thinking a bit, I realize I must give myself credit -- I often do think things through a bit. And I do say "no," too -- but, "yes," more. I do like helping others out if that is for what they're asking.
So often I see people (especially parents of young children!) who seem to have "no" on autopilot. Like they don't even hear what the child is asking, they're just ready to respond negatively. Such a bummer!
People aren't used to me saying no and funnily enough, when I do try it it doesn't go over so well! A bit disheartening, but I get it. People treat you exactly as you allow them to!