If you're local police are like mine, they won't give you an answer either way without the gun in hand. They take it to the back room and run the numbers. If it's stolen they keep it, if not you get it back, but you won't get any anwers unless they have possession of it. Go to your local FFL and see if they will run the serial number for you. Some will do it for a small fee. If you don't want to try that, here's a website that may help you, but it will only show guns that have been reported to this site. Otherwise, you'll just have to go by what your gut tells you. If it feels like a bad deal and you think it will worry you from now on, you're better off just passing on this one & moving along to the next deal.
http://www.hotgunz.com/search.php