Proof Positive and Proof Negative

I'm currently proof reading for a publisher while I wait for my next novel to appear. It's my first foray into it and although, in many ways, it's more straightforward than writing your own book, it's not without major issues. For a start, you're having to juggle a number of balls - thinking about consistency on, say, upper or lower case or chronology - which are harder when it's not your own creation. Secondly, there's the matter of correcting things. Fine, when you encounter howlers such as "could of" for "could have", but harder when you're trying to suggest a better flow and it's a matter of person taste. Sometimes you agree to differ, both firmly of the belief that the other person's wrong. In such cases, the author gets his/her way. The really great thing, though, is that if you screw up, it's the author who gets all the flack! That has to be a point in favour of proof reading.