A month or so ago, one of the people in a LinkedIn group I follow asked, "Why do self-published authors think that they can edit their book themselves?" It provoked (at this writing) over 260 comments. This is a subject about which everyone has an opinion. The reasons people gave for not hiring an editor include:
1. It's too expensive. I.e, "I have lots of time but money is limited. The only way I could justify
the expense of an Editor would be if I was making enough to afford
their services." "The new increase in my aged pension of $4.40 per fortnight doesn't quite stretch to an Editor's fees." "I resorted to editing my own work after three editors I paid did not do
what they had been paid to do. The one editor I would love to use is way
out of my league financially."
2. I don't want someone changing my work. I.e, "I want inspire others, so I feel my writing has to be my best, and not my best as tampered with by someone else."
3. I don't need one. I.e., "I pride myself on my editing skills with my own books." "Who is going to care about the book more than its author and who is
going to know better what's in the author's head than the author
himself?" "Perhaps a professional editor might suggest a few alterations to my
work, but no amount of editing could improve the number of stars
alongside those stunning [Amazon] reviews.
4. "I don't know how to find one. I.e., "How do you know the person you are going to pay this relatively large sum of money to is any good?
5. An editor? What's an editor? There seemed to be considerable confusion over the difference between a developmental editor, a line editor, and a copy editor.
6. And anyway, look at how many commercially-published books are poorly edited.
I believe every author who wants strangers to buy and read her work needs an editor. I have been confident that every manuscript I submitted for editing (or final reading) was clean. I cringed every time the manuscript returned with the editor having marked my typos, missing words, continuity failures, and more. If I did not have an in-house editor, a writer's group, and four exceptionally assiduous early readers, I would find the money to pay a professional to edit my books. I know that, as good as I think I am, if I want strangers to read and enjoy my books, I need an editor.
The second point—someone changing your work—reflects an ignorance of the system. The editor may suggest changes, but the author need not accept them. Certainly self-published author does not have to accept them; that's one reason to self-publish. And a thoughtful reader may see opportunities (or deficiencies) the author is too involved to recognize.
The people making the third point seem to me to be either misguided or delusional. I pride myself on my editing skills too, but I need help.
Finding an editor, whether developmental, line, or copy, can be a challenge, but I think you find one the way you find any good professional: word-of-mouth, internet groups, posting notices on library or college bulletin boards, whatever works. Then, as a number of people in this LinkedIn discussion suggested, you give the candidate a chapter to edit to be sure that you and she agree on style, tone, scope, price, and deadline.
Finally the fact that so many commercially-published books are poorly edited is irrelevant. It's your book, the only one that counts.