I have heard bad things about some manuscript editors.
Several professional authors have demanded that publishers not use them.
As an example: Piers Anthony had big problems over 'But What of Earth ?'
From his take on it, the editors got upset at his depiction of making a hand tools water well. He wrote down how he had made such a well himself and used it in the book. He had it published via Laser Books, who went out of business later on.
I have his annotated version he published years later via Tor Books.
While I don't exactly trust Wikipedia as a source, this article they have is factual from the other sources I have read:
http://en.wikipedia.org/wiki/Piers_Anthony