A very helpful article, thanks! I’ve been trialing editors for my current romance WIP, including industry stalwarts from The Big Four, to freelancers and hobbyists, *budget* options and the gurus who cost a pretty penny. From 9 to 5 I’m an editor myself, so it’s been great experiencing the process from a writer’s perspective. I’ve documented some tips below on what to look for in an editor (and what should send you running) , which you might find interesting.

Attention to detail is a critical skill for editors. So how do you screen out editors who might not wield a virtual red pen with the chops to catch every typo, grammar problem, style issue, and the like? You could post a job ad for an editor and subtly screen out applicants that aren’t as detail-oriented by including some fine print in the description.
The other thing I really like is your breakdown of the types of editing available. That’s what I find needs to be explained the most. Especially in business editing, you get scenarios when someone thinks a document needs “a proofread”, when it really needs a copy edit or even a heavy line edit, and you have to justify the cost or the time it takes to complete it.
Proofreading is the vital last step of the book editing process. After your manuscript has received its professional edit, your book proofreader will perform a final review to fix any remaining mechanical and grammar issues before your book is printed and published. Proofreading is not a structural edit and instead focuses on eliminating minor mistakes and inconsistencies.
It can take some time to find the right editor, so you may want to start asking around even before you have a text that is ready to send. If you know a fellow author who can recommend someone, that’s wonderful, but if not, it’s fine to poke around the websites of some editors and see who appeals to you (and seems to work within your genre). Then contact them by whatever method they request (often a contact form on their site).
It’s always sensible to follow due diligence in submitting your first draft of your book to an editor by making as fool-proof a copy as possible for you because first, it is your own creation, and secondly, a horrid draft sent your editor can end up frustrating both you and him or her. Make your own corrections to the extent you can, so that will make the job of your editor that much lighter and the end result would be a lot more effective.