Editors are paid to fix things.
Whether it's a misplaced comma, a misspelled word, or a complete overhaul on sentence structure, if we see a wrong, we need to right it or we can't sleep at night. My blog's tagline sums it up nicely:
I read books. I correct books. I read more books.One of the beautiful things about self-publishing is that the author has creative control over every aspect of his work. Overall, this is a wonderful thing. He won't have a publishing house hacking his book to pieces or changing the story line because they think it would sell better if his hero was a twenty-something woman living in the city rather than a grizzled sixty-something man who lives a reclusive life in the wilderness of Washington state. He won't have a cover designed for him that has no real connection to the book's contents or his own vision—though a quick look at lousybookcovers.com will show you why an expert is still needed, regardless of how you choose to publish. He won't lose the rights to his own work (or in some cases, his own profits) for a period of time.
The flip side of this is that some self-published authors don't see the value in constructive comments when it comes to their work. When designing a cover, an author may have an idea of what is desired, and the cover artist can present choices based on the author's vision, with tweaks here and there. Ultimately, though, if the cover artist says (just pulling a random example from nowhere), "No. Zebra stripes would NOT look good on this cover," then the author should trust that his cover artist has the eye and experience to know what he's talking about.
It's no different with an editor. The type of editing I do most often, copy editing, is pretty cut and dried when it comes to what gets changed and what doesn't. The punctuation is either correct or not. The subject and verb either agree or they do not. If something might be questioned, I make good use of margin notes to explain myself. The bottom line is this: I either know the rules or I look them up when in doubt. I'm paid to know.
I often dip my toes into the other end of the editing spectrum, though, and here's where the lines blur. I can't see something that needs changed and ignore it. I don't have the attitude that says, "They're not paying me to make the ideas flow; this job is a punctuation-only gig." I want the book to be seen favorably by the readers, and I would like to think it's a help to the author as well. If a character isn't staying true to himself and it's not part of the plot, I'll point it out and perhaps suggest an alternative. There have been times when I've said, "I know what you mean here, but I don't think this passage is conveying it very clearly. Maybe you could rephrase it this way . . ." or "This person is reacting pretty calmly, considering x and y just happened."
I'm happy to report that the authors I've worked with actually listen to me. Imagine that! They don't take every suggestion and run with it, and I try to only give ideas that are necessary, rather than changing things because that's how I would have told the story. But I've read an awful lot of books, and I can usually spot a cliché or overused plot device a mile away. If I tell a writer he may not wish to go a certain direction because too many people have done that same thing lately, I've done my part and he can choose to accept or reject that bit of advice.
That's the terrific thing about self-publishing: you can take or leave those suggestions and still come away with a product you're happy with. Rules are rules, and there aren't many ways of getting around them. Advice, though . . . if you trust the person offering it, you just might end up with something even better than you started with.