You might hire someone for a proofread, but let the editor know that you’re open to hearing from him or her if the work needs a heavier edit. The editor would need to present you with evidence in the form of sample pages that showcase what’s needed—and your job is to make sure you agree. You want to feel like an editor’s edits are polishing your work and making it shine. If you feel dread or anger, or even if you feel misunderstood, it’s likely not a good fit. At the very least you want to share your reactions with the editor so they can respond or change course.
Hm, I’m a longtime freelance book editor and have a few thoughts to share. I think one page of editing is not enough to gauge much, and that you should be able to get a sample edit of 10 (double-spaced 12-point) pages from a potential editor. You’ll have a better idea after a complete chapter has been edited, and you should have a contract that allows either you or the editor to opt out cleanly at various stages. Another thought: sometimes authors don’t know what level of edit they need, and a good editor can assess this based on reading a few pages of your ms. and spot-checking the remainder. Also: a lot of book editors (like me) work primarily for publishers rather than for individuals. It’s just easier. I know I’ll get paid, I don’t need to educate publisher clients about the process itself, and they send me regular work, so we get to know each other’s needs and preferences. Lastly, I wouldn’t really expect a newcomer editor to be able to handle a booklength manuscript very well (I was that person once — eek). If it’s someone really new, they should have had good training somewhere imo. Book editing is a technical undertaking. It’s also about knowing what to leave alone. Inexperienced people often tamper with authors’ work unnecessarily. Anyhow, I’d be happy to answer any questions.
Copy editors catch spelling mistakes, errors in grammar, and inconsistencies in your text. They know when compound words are hyphenated (or not), whether the book is ‘laying’ or ‘lying’ on the table, and whether eagles have ‘talons’ or ‘claws.’ They’ll go through your manuscript line by line for accuracy and consistency of style. A good copy editor will make sure that your voice remains intact while restructuring sentences, and substituting weak word choices for stronger ones.
Obviously there is a big difference. I actually started with screenplays (with some mild success) partly due to hearing that as long as you have a good story, the grammatical errors won’t be a big deal. Well, that was not true. Maybe if a producer liked the story or I was already established but every contest I entered always came back with feedback about the grammatical errors. Even if I won or placed as a finalist, I always received critique on that. Very little is spelling error, it was more about structure, etc.