I have been editing for many years: literary and other magazines, dissertations, mss of prose and poetry, trade novels, academic articles and books, the proceedings of academic conferences, collections of essays, etc.; and I've been a member of the Editors' Association of Canada for nearly as long. Consequently, I work by contract and charge professional fees, along guidelines suggested by the EAC.
My editing approach is straightforward: I edit according to the best professional practices that apply to the mss in question; and the author has the prerogative of accepting or rejecting my suggestions.Some of my clients' testimonials are found on this site.
As the EAC has it, an editor's job is [to try] to save the writer from her/himself, but the author is always "right" in the end.
A standard contract and technical definitions, as well as my professional profile, are found on the EAC website.
See Sample 1 for structural editing); Sample 2 for copy editing.