Actually, it's probably most of the time.
My most recent purchase is a perfect example:
1961 Fleer Jack Twyman #65
I really don't get the whole grading fad (to me it's still just a fad). But from what I have been able to gather, off center cards seem to be just about the biggest flaw a piece of cardboard can have when it comes to grading.
The total with shipping for the card was $4.24, and there is no way you would ever find a '61 Fleer (HOF'er) for that price at any card shop or show. Yet, no one else bid. Like I said, I really don't understand.
For those that care here's the back