NIP ASUS P8Z77-V Lk, $139.99 at NewEgg.
Was mounted in a case once for an hour, socket had CPU mounted once. Socket has 2 bent pins shown.
http://oi46.tinypic.com/312xq1k.jpg
What's a fair price?
As a general rule I think used PC hardware looses about 1/2 it's value when you open the box.
You best bet is to check it out during the return period so then you pay at most a re-stocking fee (20% ??) Selling it on-line you will take a muc bigger than 20% hit.
Every buyer does the same thing: He looks around and sees what is the best deal. He never thinks "How much money does this seller deserve?", No he looks for the best deal he can find. So to sell the MB you must position it as the best deal some one is likely to find. And you are competing with new MBs of various different brands.