Editing

Today I am editing a minister's book. I didn't necessarily apply for this job. Actually, I applied to edit a dissertation. However, the woman writing the dissertation wanted me to edit this book for her minister as well.
It is very difficult editing a book on Biblical doctrine when you don't have the same doctrine. As an editor, you need to smooth content (this is not true in all cases, but it is true for this particular job). Sometimes people write things and do not realize they are not coming across as they probably want them to come across. But you also should not change the meaning of something that the author wants to leave that way.
In some cases, like when you are writing fiction for someone, you can write or edit something that you know is completely false - after all it is fiction. Usually, I will send a quick note to the employer and inform them of the error and then explain why I am going to keep it.
Non-fiction is another story. In most cases, I will let the author know their is an error and I ask if they want me to fix it. I have been quite stubborn in the past about not writing stuff I know is false. However, how do you tell a minister he's wrong about something? Especially if it is something that could be a matter of opinion?
Needless to say, I do not generally bid on non-fiction Christian books - even just to edit. But, I bid on the dissertation and this is a side job of that. Sigh.