The single most decisive factor should be the quality of the edit itself: Will this editor help improve your book? In order to assess this, nothing beats a sample edit (even if you have to pay for it). Testimonials and credentials (such as experience at a major NY publisher) can help you narrow your list, but you should submit the same sample to a variety of editors and compare their work side by side. Some editors will push too hard, and some won’t push hard enough; some will simply “get” your writing, while others will seem to speak another language entirely. In my experience, the editor’s résumé is far less revealing than the quality of the sample edit. In fact, the higher an editor’s pedigree, the more reluctant the editor might be to provide a sample edit. Don’t be afraid to insist: no one should expect you to invest in a car without a test drive!
I immediately noticed upgrades to certain passages that had hung me up. There are quite a few spots that I had rewritten over and over again but felt they were just not quite right and you seemed to find them all and make them flow perfectly in no time! I am very excited with the new work that you have placed before me. Again, excellent work and thanks. Looking forward to continuing to work with you!
Check out freelance websites like UpWorkor even a great site called Scribendi. (Warning: if you source an editor from these sites, make sure you hire another, professional editor to go over it afterward. There is no way to know what you are getting otherwise. Just because the draft comes back better than it was before, does not mean it was well-edited!)
In fact, Pressfield writes, “Resistance is experienced as fear; the degree of fear equates to the strength of Resistance. Therefore the more fear we feel about a specific enterprise, the more certain we can be that that enterprise is important to us and to the growth of our soul. That’s why we feel so much Resistance. If it meant nothing to us, there’d be no Resistance.”