I don't know if other editors get this, or if I'm just an anxious person. Before I have even started reading a fresh manuscript, I start worrying about how the author will receive my comments. Not even criticisms; I just worry that I might not be able to communicate my findings.
Worse than that, I worry that I might not even find anything to say. I'm sure that's hard to believe—others tell me that I always have something to say.
The biggest worry is that as a literary editor, I'm looking for something beyond errors and issues, holes and inconsistencies. I'm looking for opportunities and improvements. Supposing the book is already as good as it can be? Supposing the author already knows that?
So far, I haven't edited for someone who really knows how good they are. I've edited for really good writers, they just haven't been aware of it. I know, because I'm at that point myself with some areas of editing, that it is possible in writing to know exactly what you're doing – to be conscious of all your choices, techniques and devices.
I suppose one day I shall edit for such a writer, and I shall have to say to them: "um, you don't really need me, but I did read your book and think very hard about it, so, you have to pay the full fee anyway."
Really, that's what it comes down to: the better your writing, the less value you're going to get from a literary edit. And I want to give value. And also, I want to get paid.
This is in part why I like to be paid in instalments. From time to time I underestimate the amount of work that a text will be. When I do, I suck it in, and get on with it. Less often, though it does happen, I overestimate. In those cases, I can tell the author to knock a chunk off the final instalment or even forget it altogether.
Making sure that the value I give matches my fee is not just about professional or personal honesty. I see it as a socio-economic responsibility. Overcharging devalues.