I highly respect editors, and some do great, and others do mediocre work. I always thought you paid a lump sum (that is the overwhelming majority of the cases, I do believe) and they just polish the grammer, spelling, and understand the flow of the book. In no way, should an editor change the "ideas" of the book.
This is something that I ensured, that my ideas would not change with the editing process during the first two books that I sent in to a publisher. Although, the editing was done at the publishing house. The publisher gets a cut into the book, anyways.
Point being, do we give a Doctor, Nurses, royalties on the birth of our son? For the rest of their lives, for helping bringing them into the world?
The book is the authors creation. If it was not for the writer, there would be no book. There is also no guarantee that the book will succeed or fail. The writer takes, 100 % of the chance. The editor takes a lump sum payment for his services to edit, usually in the approximate 1200 dollar range, but the averages vary depending on where you go.
I have nothing against giving credit to an editor in the front of the book for his services. If an editor feels he has changed the true direction of the book, the main gist of the book, or changed over a heavy % of the books feeling of the writings, then I would feel he should receive a royalty. This would have to be a small % of the book, or a half % if he changed half of your book, for instance. But it must be negotiated before the changes take place. If the editor has nothing in writing to prove massive changes were made to the writing, then he should just accept his lump sum payment.
But just for polishing, grammar, spelling, he is doing something like a mechanic that services your car is doing. Pay a flat rate, but he does not make money per mile you drive.
Till next time..