Just about all successful self-published writers I know (including one making six figures off Kindle sales) hire both a professional editor and a copy-editor for their books. This money comes out of their own pocket to ensure quality.
Editing is a distinct skill, it's about seeing the story the author is trying to tell and finding places where that story is covered up. It's not the same as a critique and it's the very rare person who can do it for themselves. Any beginning writer that says "I don't need an editor because they'll screw me up," has never worked with a good editor or they would know the value of good editing.