But $ is not what determines one's filing requirements or reporting position, is it?  Unfortunately, incorrect reporting most often comes with a cost, in one way or another.  The only way to avoid that is to have the return done right the first time (and, often times, with proper planning ahead of a significant transaction). 

There is nothing unethical about billing a client for the fair amount of work that needs to be undertaken (unless the additional work was the result of one's own fault) but that also doesn't negate the discretion a practitioner has in setting one's fees under different circumstances.