There are certainly some questions I'd ask about the Sauer that started this thread. That being said, comparing it to the 16ga mentioned on gunbroker . . . that's a gun that needs a total "facelift", wood and metal, to make it look as good as the gun Greg posted. Forend may well be a replacement. (I don't see any indication of checkering.) It's likely an extractor gun vs ejector, and it's a lower grade gun to begin with. Comparing the two is like a beat-up Sterlingworth to a nicely redone Fox AE. There's a reason for the difference in price. . . not to mention that the guy selling the gun Greg posted knows how to take photos that really show you something. (Bad photos can hide a lot of sins.)
Here's a personal recommendation: If you're looking for a good, basic used German gun, keep your eye on Mark's Born Again Birdguns (one of the advertisers here on doublegunshop). His prices are reasonable, and Mark is a talented gunsmith who makes sure his guns are right before they leave the shop. His inventory is a bit low right now, but that's because he prices guns to sell--and they do sell.