First, I’m an author, not a copy-editor, and I’m not selling any services. For my first four books I didn’t use a copy-edit as it would have cost me around a thousand pounds to do so per book, and I didn’t think it was worth it. Now I have a large publisher behind me, and have just had a copy-edit done for me (for free), I’ve basically changed my mind. 

The last stage before your words are locked in forever
When your manuscript is heading for publication, after you’ve done all you can to polish it, there are always two remaining items to consider. Copy-editing and proofing. Proofing can be done mostly automatically via grammar and spell-checking, and having careful readers go through your manuscript. Copy-editing is different, though. 

So, what is copy-editing, and why is it a good idea? 
Here’s a formal definition:
The goal of copy editing is to ensure that content is accurate, easy to follow, fit for its purpose, and free of error, omission, inconsistency, and repetition.[
Here’s another way of saying it: A good copy-edit will:

  1. Smooth out your prose, making it flow better and read easier, and remain fresh (e.g. by avoiding repetitions)
  2. Ensure consistency throughout the book – not just names and places and timings, but what people know or should know at various points in the book
  3. Making sure your character stays true to their nature (e.g. asking whether a particular character would really say such things?)
  4. Pointing out (usually minor) plot holes. The reader can often bridge these gaps, but will be aware of them. 
  5. Point out strange, antiquated or specialized usage of language that may jar with the reader. These things can stop a reader, making then think ‘huh?’, and either make them get out their smart-phones to try and work it out, or just stop them reading.
  6. Identify where something should have been explained earlier in the text
  7. Detect position or layout anomalies – e.g. someone stands up but we didn’t know he was sitting down – or an action scene only the author can visualize
  8. Cases where ‘less is more’, e.g. where the author had successfully made a point but then carried on, weakening it.
  9. Noting where machinery or the environment seems to have been forgotten, e.g. I originally had the skipper of a boat try to seduce someone, and he (apparently, because I ‘said’ nothing) just left the controls with the engine in gear. No real skipper would do that.
  10. Helping to isolate the best word, or as the French say, le mot juste. I’d said that someone had disappeared, when in fact they had been abducted. An important difference. 
Why can’t authors do they down copy-editing? 
Of course we all do, to an extent. But we are too close to things. In our heads the characters and their motivations are perfectly clear, as are things like locations and what is going on around the characters. But this 20:20 vision of what the novel is supposed to say sometimes makes us blind to what we have actually committed to paper.
I belong to a writers group in Paris, and we all review each others’ work. But an author is not usually a copy-editor, nor vice versa. These are different skill sets. Of course, the more people who read your novel, the better, but even so, a skilled copy-editor is likely to come up with new issues that do need to be fixed. My book had been read by nine people (four readers, four authors and an editor) before it was copy-edited. 
Copy-edit as an acid test – is your manuscript really ready?
Another important reason for a copy-edit is to gain feedback. Not whether they liked it or not, but just how many comments or queries did you get? For mine, which had already been reviewed and edited, I had around a dozen queries, for a 97000 word manuscript (I’m discounting the simple grammatical corrections, of which there were a couple of dozen). If I had received fifty queries, I would have realized it simply wasn’t as ready as I’d thought. 
Eliminating reader potholes
Each of those dozen queries contained something that made me think – okay, I need to change this. A couple of times I replied to the copy-editor “good catch” (or ‘nice save’). I want my thriller to be a page-turner, and it can’t be if there are potholes scattered along the reader’s pathway. It only took me 2.5 hours to go through the copy-edits for the entire manuscript, make the changes, and then send it back to the publisher. Probably the best 2.5 hours I spent on the book since I started it.
But it costs so much…
But what about the cost? If you have a medium or large-sized publisher they should do copy-editing for you, so just sit back and wait for those track changes. But for many writers, particularly those self-publishing, an extra 600-1000 pounds/dollars/euros seems a lot, given that you have to also pay for formatting, front cover, etc. So, is it worth it?
If you want to be serious/professional about your writing, I’d say ‘yes’.  Either of two things will happen. One, you’ll get comments and think, oh gosh, yes, I need to change that, or else you’ll get very little, in which case you can be confident that your novel is in very good shape. 
Another way to think about it is to reflect on how long it takes to do a copy-edit. This is no speed-read with a glass of wine in your hand, but is a very careful reading, making notes, continually referring back to earlier sections for consistency checking, etc. Think about how many hours it must take to do a copy-edit.
Where do I find a good copy-editing service?
Okay, so this is where I have to say I don’t know, as I’ve never paid for one. However, two literary services I trust in the UK are Writers Workshop and Cornerstones, but hey, shop around, find other authors who have had copy-editing done and ask them who they’d recommend. 
Final thought
Think what a sprinter would pay to shave off half a second. You’ve written the best novel you possibly can. Don’t sell yourself or your novel short. Make it that little bit better.
Good luck!
Sixty-Six Metres is released 25th August