Lets say your car broke down.
You take it to two mechanics.
Mechanic A is national firm that hires just about anyone as their mechanic. Just do a search on monster. Hundreds of positions. They don't make the cars though, they just fix them. In fact, they've never actually set foot in the manufacturing plant. Your mechanic hasn't worked on your specific car before, but once saw one drive by. Mechanic A test drove your car and scored it a D. He knows that if he fixes it and it doesnt score better next time in the road test, you will be mad and will tell people how crappy he is. He therefore realizes that giving you an artificially low score increases the chances that your car will get better than a D in the real road test, given by Mechanic B, even if his work is so poor that it's a tragedy a firm like his can stay in business.
Mechanic B is a national car manufacturer. They not only fix the cars, they make them too. Oh and this mechanic designed your particular car. In fact, he's fixed about 657,173 of them. He says your car is a C grade car.
Which do you believe?
I believe Mechanic B.
Hint: Mechanic A is Kaplan
Hint: Mechanic B is GMATPrep
Relax
chill out
sleep
and slam dunk it.