One of the things I have learned over the years is that I suck at editing my own work. I’m not bad at editing other people’s work, at least for content and some copy editing. I am still weak at line editing (warning to all those who think you will get that at New Libri Press, my publishing company). Two out of three is not bad, but you may want to pay for some line editing at the very end.
Editing is not easy. I really like this video: by John McIntyre at Loyola University, professor on editing. He tells it like it is, boring, same thing over and over, etc.
Now, most of New Libri’s authors are good writers. They know their grammar. Why would an author need editing, if they are smart and talented? Because we don’t see our own mistakes. I can read the same chapter of my own work ten times and not see the mistake that a friend of mine sees instantly. Even editors make mistakes, I might add. I guarantee you that I can pick up almost any book, open it randomly, and within a few pages find an error. But, not in my own book.
I remember opening up a book written by a professor at my MFA program (who shall remain nameless). He was a stickler for detail. He taught English at a university, as many literary fiction authors do. He sometimes treated his graduate students as if they were undergraduates, partially because he knew we came from all different backgrounds. My co-founder and I were simply examining the book cover, layout, and blurb. The outside marketing, so to speak. We randomly opened the book and found two errors on the page we opened it on.
I think, unfortunately, that more and more readers are forgiving of crappy editing because they are getting their books for free. I hope that trend changes. Perhaps, over time, it will, as some sort of accurate system takes hold (and that is not customer reviews at Amazon. See Paid Book Reviews and Explosion of Self-publishing).
Until then, you need to decide if it is worth getting the editing done. You may, or may not, recoup your costs, but certainly you will know the best product is out there.
Choosing an editor is a different issue that, maybe, will get covered at a later date.
A couple of reminders:
Critique partners are not editors. They are craft focused beta readers, who are honest and have ideas.
Beta readers are not editors, they are sympathetic readers who will tell you what they like in the story.
Not all editors are good at all three types of editors.