I"ll try to help you out here...
What year is it made? What length barrel? Any cracks in the wood? How is the bluing/wood finish? has the stock been cut? round knob or flat knob? What choke? Does the barrel have a vent rib,matte rib,solid rib? Belgian or Japanese made? 12,16,0r 20? is it a 12 light,mag, or standard? 16 standard or sweet sixteen? If it is a sixteen, is it 2 3/4 or 2 9/16? 20 standard or magnum? If you find out these things we will have a good starting point in attempting to figure out what it is worth. I hope this helps a little.