When you hire a writer or editor, you want someone who knows the English language and can make it work for you. Not someone who can make it work for an audience a decade younger than who you're targeting, nor someone who slaughters it to the point that you have to hire someone to fix it for you.
You want someone who can deliver what you've ordered, in the time frame agreed upon. Someone who won't flake and vanish on you. Someone who will act professional and produce quality work.