Editing is one of those skillsets that many people claim to do well but which few actually do. And while it’s probably the most important service an author can solicit (second only to book cover design), it’s often undervalued. Furthermore, most authors have no idea how to assess an editor’s work, and the result can be catastrophic, ranging from an editor who introduces new errors to an editor who changes the intention of your writing.
A copy editor or line editor focuses on improving sentences and grammar, as well as suggesting other ways of rephrasing ideas, and providing comment on anything else they pick up. Non-fiction books often use multiple styles, for example, chapter headings, sub-headings, action points, bullet points, call-outs and examples, so these will be examined at this phase.

This is basically like the “Quick Kill” service – or proofreading on steroids, and again we’ll hack, slash, rewrite, fix, tweak and improve anything we can, but this time we won’t comment on the bigger picture, and we’ll really hone down on the little details, eliminate repetition, trim the writing, and make sure everything is as good as it can be.
Understanding how to find a children’s book editor is a key step when producing a strong piece of children’s literature in the hopes of publishing your book. There are tons upon tons of children’s book editors available and the range of editorial services is wide and deep. Because there are so many editors to choose from, knowing what editorial services you need is the first place to start.
While you may (or may not) be correct in your assumptions, your tone in general is rude, and disrespectful. If you are indeed a true editor of distinct taste and experience, you should not feel the need to bad mouth others for their thoughts and opinions. Show a little decency, and realize that you are indeed speaking to a human being, who probably has thoughts and feelings, and is in my opinion, a much more intelligent human for having the intellect to not attack someone verbally for their thoughts. No one needs you to be rude, or asked you for that matter.
Regarding your last question, I know of no editor who gives a money-back guarantee for occasional errors that happen to slip through or for a different opinion by a later editor. I’m afraid such things are just the nature of the publishing beast. But by having a shorter portion edited first, you will get a decent feel for whether someone is the right editor for you, and will be able to be confident in his or her work on your entire book.