Start by identifying the level of editing your manuscript actually needs, then compare editors on scope rather than headline price. Ask for a written proposal that states the word count, editing level, deliverables, schedule, revision or query process and what is not included.
Choose the right editing level
Developmental editing, copyediting and proofreading solve different problems. Paying for the wrong stage can waste money and delay publication.
Ask how feedback is delivered
Confirm whether you receive tracked changes, an editorial letter, style sheet, comments or follow-up questions, and whether a sample edit is available.
Protect the production schedule
Allow time for the author to review edits and make decisions before formatting or cover-spine calculations are finalised.