You want the right editor, the one person that will 'get' what you're trying to accomplish and who can fulfill that vision. Fair enough. But editors have needs, too, as odd a statement as that might seem. I've been doing this editing thing for a while now and I've worked with hundreds of people on various types of projects: manuscripts, textbooks, book proposals, poetry, short stories, user guides and so on.
Before you begin any new project, you discuss in great detail expectations and desired outcome. As the client, you do need to educate yourself to some extent on what kind of editing you require. I take the time to explain at great length to many people the types of edits available and the process as a whole, but still, it evades most, mostly because they are too eager to get the project done and have it looking like a million bucks -- because an editor will make it perfect, right?
Um, that all depends on how much money and time you've allowed said editor. With enough time, a project can be whipped into great shape. A perfect product? I don't think that exists -- ask any published author who finds typos and such in their books. Typos happen. You as an individual don't have enough money to fund the kind of perfection you are looking for: the man hours and sets of eyes required to ensure a project is as close to perfect as possible are astronomical and therefore pricey. At Harlequin (when I worked there), a manuscript was looked at by at least 10 sets of eyes before getting printed. Love them or hate them, they follow a rigorous process to ensure an error-free finished product. But most of us aren't major mass market paperback publishers and so our pockets aren't as deep. (For defintions of types of edit, see http://www.editors.ca/hire/definitions.html.
So, my ideal client is aware of these pitfalls and is ready to deal with it by coming to the table with a reasonable expectation of what can be done given the budget allowed. Another 'nice to have' is a client that actually knows what they want. Please don't come to me and say you need me to bring something "to life" and not be willing to pay for the hours necessary to do that. A substantive edit alone won't bring something to life - rewriting will. Make sure you need an editor and not a writer first. Make sure you know what you need so that you aren't disappointed.