As others have said, the vendors don't know if it's a 'sharp' copy or not - they sell what they receive from the manufacturers in the boxes. With that said, every so often a bad one sneaks by quality control at the manufacturer, and that's why it's smart to buy from reputable, trustworthy vendors such as Adorama or B&H. They have good return policies and will always make it right for you. Both of those dealers have customer service reps here on POTN who monitor threads and pop in often to make absolutely sure that things are taken care of.
Buying from the 'fly by night' vendors is a good way to get burned with something like a 15% restocking fee for a defective return - or worse yet, no return policy at all! As has often been said - if a deal looks too good to be true, it often is. I'd rather pay a fair price at a reputable dealer and know things will be taken care of if anything goes wrong, rather than saving a few bucks and being left holding the bag if something turns out to be defective/damaged.