What To Look For in a Freelance Editor?

I plan to independently publish my book on retailing and am looking forward to the point when I finish and need to find an editor.

Do I need to find someone with editing experience in my genre? Is this type of editing different than simple grammar checking?

I have a friend who is the editor of a trade publication and he has done a nice job editing my article submissions but I am not sure if he is willing to edit without also being the publisher.

Is there a list of freelance editors on AbsoluteWrite?

Thanks,

Steven