The most knowledgeable folks I know are on the P38 forum. Be prepared to post photos for an honest opinion. The database they have is the most complete one that I know of. Registration is free and you can easily upload photos from your computer. Value depends on condition, rarity and most what a buyer would pay for it. I have a pre-war PPK (1939) my Father brought back from WW-II with capture papers and I intend to hand it down to my Daughter.