I cannot speak for overstockdigital.com, I've never used them, but if its too good to be true.... you know the story.
In general, places with prices significantly below normal play games. You order, then they call to 'confirm'. During that conversation they will try to sell you something 'better' at a much higher price. Or they might say this camera you ordered does not come with a battery or a charger or other essentials. If you stick with your original plan, they will come up with other problems. Suddenly it will not be out of stock or it will take 3 weeks to ship, etc. Good chance what you wanted will never be available. Also, if they are not an authorized Nikon dealer, you will have warranty problems. But I really think it would not get to a point where you got the camera in hand for that price.
Try googling overstockdigital.com to see if you can find any dirt.