“My books have very complicated formatting with over 100 illustrations each, external links, and numerous bulleted lists. None of the formatters I contacted would even take these on but John said “No problem!” He completed my original three e-books quickly, for a more than fair price, and they look great. I have no hesitation recommending Ebook Launch’s work to other e-book authors!”
Another online editing service is Scribendi, which has over 300 experienced and educated editors. They've been around a long time. With this service, you decide how fast you want the book edited and how extensive the edit should be, then they match you with an editor. You don't ever actually meet the editor, but rather work through their customer service team. Their prices depend on your requested turnaround time and word count. You can get a free quote here.

That said, I don’t recommend going to publication, particularly if your book is intended as a revenue-generating venture or as a vehicle of professional promotion, without making sure that someone with an eye for detail has gone through the entire manuscript and ruthlessly noted every typo, every spelling error, every misplaced comma, and every ambiguous sentence.

Even if you wrote the book in your free time, this is my day job. The per-project cost many new authors would consider “manageable” would, if broken into an hourly rate, end up paying editors less than minimum wage. They don’t intend to pay what someone could earn making french fries; they just greatly underestimate how much time must be invested in editing.
ROUND ONE: We’ll start with a manuscript review – a quick read-through to identify any major problems, boring parts that need trimming, conclusions that can be made stronger, suggestions for rewrites, plot improvements or problems, story arc and structural analysis. We’ll ask lots of questions and provide tips and recommendations. Your editor will be like a personal writing coach. We’ll send an editorial report on the big issues that can be improved. After you’ve rewritten to your satisfaction, we’ll move on to part two.
That’s a great point about other disciplines. Why should writing require some outside arbiter? Is it because these other disciplines consist in crafts that require significant training, whereas anyone who’s literate can start writing a book at any time (and therefore, the threshold for entering the medium is much lower)? I do hope you’re right about learning self-editing skills. I actually just made a YouTube video about how to self-edit: https://www.youtube.com/watch?v=3mmLEuH9x28
Next, I check their work history to see what kind of projects they have been working on. For example, if I’m hiring an editor and I see that 8 out of their last 10 projects had nothing to do with editing, I will probably pass because it means they either don’t enjoy editing work or they aren’t able to find enough of it on Upwork, which should not be a problem for a highly skilled editor.

Obviously there is a big difference. I actually started with screenplays (with some mild success) partly due to hearing that as long as you have a good story, the grammatical errors won’t be a big deal. Well, that was not true. Maybe if a producer liked the story or I was already established but every contest I entered always came back with feedback about the grammatical errors. Even if I won or placed as a finalist, I always received critique on that. Very little is spelling error, it was more about structure, etc.