A great post by the Tuck School at Dartmouth, where I was an exchange student: http://www.tuck.dartmouth.edu/mba/blog/so-you-want-to-work-with-an-admissions-consultant

As someone who does admissions consulting myself I especially liked this:-
"A dead giveaway is when you accidentally submit a draft copy of your essays with the consultant’s notes all over them. Rare, I grant you, but it’s happened. More commonly, something in your application raises doubts in our minds. We notice that, although your Analytical Writing Assessment, TOEFL or IELTS score is low, your essays are perfect. You seem to know the questions we’ll ask in the interview before we ask them. Now, you could have done this all on your own, but it gives us pause. In a competitive applicant pool, don’t give the Admissions Committee a reason to weed you out.
"

I can't believe that somebody would submit draft essays like that!

The latter point is quite interesting because it points out the risk of being 'over-prepared.' Having worked with MBA candidates in the past, my impressions are that there are some people who are so eager to get into a program that they're willing to go to great lengths to control everything they can control.

Personally I'm happy to give feedback on somebody's essays and point them in the right direction, but I can't tell them what to write.