What do you want to know?
Depending on its condition (and of course a willing buyer) it should be worth between $575 - $800. You might want to watch for similar guns at www.gunbroker.com to see what they are currently selling...
12
20 gauge is really little. 16 is a little bit bigger then a large safety pin. If you wanna make sure ask a tattoo artist or body piercer.
Need a detailed description of all markings, condition, finish, box, papers, accessories, engraving, type of action, etc..
You will have to shoot all of them through your shotgun to see which one(s) it prefers.
2011 Honda CR-Z Hybrid Review
2011 Nissan Quest Overview
Measuring for Gauge
Boating Tips - Gauges and Panels