Book doctors
This is an iffy area.
In general, if you actually need help with the kinds of issues that would be dealt with by a copy editor, I'd suggest you join writing workshops or critique groups instead. And it isn't a bad idea to try workshops/groups out just to see if your tech skills are as good as you think they are. (Books such as Browne and King's "Self-Editing for Fiction Writers" can also help.)
If your writing is already professional quality--if workshops uniformly praise your prose, and reputable agents write you letters back saying that it's almost there but not quite, and please feel free to try me again with anything else you write in the future...THEN you MAY want to consider a book doctor for a story memo.
An agent who read my first novel asked me if I'd ever considered a book doctor. Somewhat indignant, I wrote back that I didn't need to pay for grammar lessons and thought that it would be a waste of time.
She replied that the problem with my novel wasn't the writing, but the story line--I had scenes included that were good, but could also be dispensed with, and that I had too many plot lines running at once. She emphasized that this--high-level structural issues--was what book doctors were really for. I thanked her and ignored her advice, but on a later book, when I had it polished and ready to go, I consulted a book doctor for a story memo (also called an ms overview, and various other names).
A story memo is typically 5-10 pages, single-spaced, talking about broad issues like like pacing, story points, how the style works (or doesn't) with the narrative line--the kinds of big issues that I suspect acquiring editors used to deal with back in those legendary days when editors acquired books expecting to do substantial back-and-forth.
This kind of service will cost you about $2 per page of manuscript, so a 500-page novel will set you back about $1000. Not cheap, not cheap at all.
In my case, I think it was money well spent. The editor identified a few places where he though scenes could be cut; a couple where he thought things lagged; a place late in the book where he thought I should push it a little harder and make the scene bigger.
Not very specific advice, but well-reasoned and authoritative. And I didn't end up taking all of his advice, because, frankly, I disagreed with some of it.
All in all I ended up losing a chapter, switching the order of two others, and adding a couple of big scenes. Net result: manuscript probably changed by less than 5 percent. Did I think it was worth it? Yes.
Did I immediately get offers of representation from agents? Yes--but I think I would have in any case. But what I sent them was a manuscript that had not only been polished to the best of my ability, but also had a test-screening in front of a skilled, articulate reader with no vested interest in preserving my feelings.
THAT SAID, however--this is an area teeming with scammers, and, almost as bad, with amateurs and incompetents. And the linkage between scam agents and scam book doctors is the stuff of legend.
So how do you find a good book doctor? Heck if I know--it's like trying to find your soulmate. Word of mouth, recommendations from people with no vested interest; folks who have written well on editing and writing who are in the business...even if you check bona fides, it still ends up being a crapshoot (maybe the editor just doesn't like your style of book). I was very cautious, very skeptical, and I also happened to be lucky.
I think it can be worthwhile, but caveat emptor.
