There seems to be something half-way between beta-reading and development editing. I think it’s right for many new writers — I’m just finishing my first book, and was not about to pay a real development editor, but beta readers weren’t engaged enough (especially friends unwilling to point out the negatives). But it this kind of editing doesn’t really have a clear name.
Are you writing a picture book? A chapter book or easy reader? Is your book for middle grade readers or young adults? You may not know for sure! What age groups will be reading your book? How many words should your book have to be age appropriate? What themes or topics are typically relevant? These are some of the more generalized questions your editor can answer for you.
I like the idea of embedding “fine print” into the initial email. I also think it’s a good idea for an author to check references; the questions Val suggested are great. Third, as another commenter said, an editor can give the author a general assessment of their book, which will help the author decide if that particular editor will be a good fit or not.
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.