Recently we were editing a piece and the author was “surprised” that we didn’t catch a number of errors that a friend of his caught. However, when asked what those errors were, none of them were grammar, or spelling, but all were subjective. Word order. Word choice. We (my co-editor and I) laughed a bit at this. We didn’t catch it because both of us liked it the way it was.
Editing is subjective, especially meta editing, but even line editing. Some editors hate point of view changes within a chapter, others don’t mind if it is done right. Some will harp on lack of detail in areas where another will think too much detail slows down the manuscript.
An editor provides a subjective critique of your work. It is up to you to decide if that subjective critique is good. Agreeing with it, or not, is not the best criteria. Rather, if after a few days of stewing over editorial comments you find yourself saying “I can’t believe that he thinks that, but I really want to make it clear to him without changing my tone too much,” then your editor has probably done his job.
Even line editing is subjective. When do you break the rules? Does it work in this case? Was there a joke I missed in principal versus principle in this short story?
In general, and this is my subjective criteria, if you find yourself listening to 40% of what your editor tells you, then you editor is doing a good job. Listening does not mean doing exactly what he suggests. Listening means you act on the suggestion in some way.
An editor will not make terrible writing good, no matter how great the plot is. An editor is not a co-author.
With a publisher, it is very hard to tell where the hand of the editor touched the manuscript. In general, with a publisher, look at any books (even if it is a small publisher with only a couple of books) and if you like the book, than there is a chance the editor did his job.
For independent editors, many will offer a free analysis of 5 pages. This is a weak sample, but better than nothing. For a full length novel, the meta edit may take reading 50 pages to form an opinion. If they are established, the job is easier by examining the finished work of cited clients. However, many good editors are not well known. Just like an unknown author, it takes a bit of time to break in. BookBaby has a decent article on independent editing. Of course that is my subjective opinion.