There is no one-size-fits-all editor. Hire a professional suited to your field/genre. When interviewing candidates, clearly communicate the required services. Editorial terms vary. However, a general breakdown follows.
Manuscript Review: Examines purpose, audience focus, content development, readability, style, tone, voice, need to rewrite, structure, cohesiveness, flow, and word choices. (In fiction, also examines hook, characterization, point of view, conflict, plot, setting, time frame, awkward passages, and detail.) A critique does not involve proofreading, copyediting, line editing, developmental editing, or rewriting. It is an overall review of the text so the writer can address major issues to shape the manuscript.
Developmental Editor: Addresses format, logic, structure, style, tone, voice, cohesiveness, clarity, flow, text to rewrite, information gaps, and unfocused copy.
Heavy Copyeditor: Performs basic copyediting. Addresses style, tone, voice, readability, logic, structure, cohesiveness, flow, consistency of content, elimination of ambiguity, triteness, wordiness, jargon, redundancy, appropriate word choices, context, and smooth transitions.
Basic Copyeditor: Addresses grammar, usage, punctuation, spelling, capitalization, mechanics, cross-references, and order.
Proofreader: Checks basic grammar, punctuation, capitalization, spelling, and mechanics. Cross-checks table of contents, tables, lists, and other matter.
Note: A manuscript review is a wise investment, especially if you’re a first-time author. It’s a reality check on how much work your text requires before you turn it over to an editor. Revise, revise, revise.
Question: How much rewriting do you do?
Hemingway: It depends. I rewrote the ending of A Farewell to Arms, the last page of it, 39 times before I was satisfied.
Question: Was there some technical problem there? What was it that had stumped you?
Hemingway: Getting the words right.
—The Paris Review Interview, 1956
Credit: Image of Ernest Hemingway by Lloyd Arnold [public domain] via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:ErnestHemingway.jpg