Freelance editors, especially when starting out, often take whatever work we can get. There are a lot of people who need editing help out there, but a lot of them have strange ideas about how the relationship with an editor should work. In editing, "the customer is always right" doesn't cut it—because the real customer is the ultimate reader of the material, not the writer. But a surprising number of writers don't acknowledge that.
Some of those writers (or publishers, or students, or whoever) have such set ideas about what they want that they become clients from Hell, second-gessing every decision or imposing weird conditions on an editor's work. Not coincidentally, those people are also usually unwilling to pay a fair rate. They aren't worth keeping around.
Ultimately, if a client requires you, the editor, to maintain his or her bizarro style, grammar, and punctuation, and you find it intolerable because you know it will be disruptive for readers, then it might be time to get out. What else, in the end, are you there for? People hire you to be an editor (at least they say so), and if they won't let you edit, you have the right not to let them make you do something else, such as acting as a foil for spaced-out ideas about written text.
Here's another way to look at it: a client who refuses to let you edit his or her writing using fairly standardized rules—which include rather a lot of leeway anyway—isn't really asking you to edit written English at all, but some hybrid pseudo-language based on English, one (for instance) with way too many commas, an indecipherable choice of font, and German-style capitalization of every noun. That is not your area of expertise, and it's not a large enough market to justify your making it one.
One of the best lessons I've learned in becoming a professional editor is how and when to say no. Especially, "this is what I charge, and I do not accept less." If you really need money, there are less stressful ways of getting it—I've busked in downtown Vancouver for change, and I find that far more pleasant (and more lucrative, per real hour of work) than some of my worse editing clients. (I don't like rolling coins much, but that's just menial, not actively unpleasant.)
In general, people who fight on rates will fight about everything else too, or be otherwise difficult. When I started standing firm on what I charge, and on what I do, I was surprised at how quickly the annoying clients went away.
The same people who think nothing of asking an editor to accept half of what we normally charge would never expect to walk into a new car dealership and offer half the sticker price of an automobile.
Well, maybe they would, but they wouldn't leave with a car.