Book Editing Question

So, the nagging question that has been on my mind is whether which is better? Pay a professional editor or use a personal contact who is very good at editing but who is not a professional in the field.

So far, I’ve been using the later for several reasons.

1. We argue about sections of my books and whether they need to be there at all.
2. How to improve the story by helping to rewrite sections, large and small, while still keeping the intent of the section.
3. We can work together editing  regardless at any time of day, even well into the night or first thing in the morning. Even before my morning coffee (ah, who am I kidding, not).
4. By using someone I know and trust, we can discuss the bigger plot lines, intent and direction of the story along with a host of a number of little things that I can’t think of right now.
5. We can discuss future story lines which I can turn into an outline for another book.
6. Of course, the usually finding and correcting spelling and grammar errors.

The big question on my mind is this.

Does using a paid professional editor significantly improve the end result which translates in more sales?

What do you think? — I really want to know.