I've been in touch with countless freelance editors and gotten sample chapters. Some are of better quality than others.
I'm left with a major question. Most list books they worked on that were published. The more, the better they look. Looking more closely, however, many are Indies (which I consider padding their page). Some have been with specialized publishers: Christian presses, special interests, etc.
Other than a single, sample chapter, how can you judge how well an editor does developmental/substantive work?
I also contacted EFA and asked what qualifies their members. No reply. Just sent a second email.