Selling to a dealer can lose you a great deal of money.
I was at a local well-known camera outlet last week to pick up a wide angle lens and spotted a D3X with 17k actuations advertised for just under £4k.
Out of interest I asked what they would give me in a trade for my mint D3 with under 1k actuations and was told £1.5k - now obviously they make a profit, but the margin of loss against a private sale is just too large to contemplate unless you are desperate/flush with cash.