There are two people on this earth that get free editing for life from me. That is because they are my colleagues. They are fellow writers, but are more than peers. We have history. We have an ongoing relationship. We have a mutual understanding of each other and our work.
Editing my colleagues' works is a professional courtesy. I would do it for them and I know that they would do it for me. I'm not going to charge them like they're some random chump. I do it because I respect them and because I like them.
This is not to say that everybody else on earth gets charged every time. Certainly my parents get my edits, but that's mostly payback for them raising me and not leaving me in a ditch in Florida.
I also will edit my friends' works if it's something not terribly long, (after all, I do it because I care) but that's in moderation and when I have the time. It's similar, but not quite the same.
Sometimes I like to use the classic line, "your money's no good here." My colleagues are invaluable, and I will always make sure they know that. Professional courtesies are one of the ways I do that.