Gander occasionally has good deals on used guns when the employees don't know what they're buying. I once purchased a rare 9mm J frame for less than 1/3 its value at gander.
I've kicked myself a few times through the years for not buying the ones that slipped through their cracks. Passed on a Marlin 30/30 for $219 several years ago, and a Ruger .41 magnum for $299. As jdmack said, the pricing guy misses one now and then.
Typically, Gandder Mtn. sells used guns for nearly the same price as new. If it is older they will price it like it is a collector, even though it is only a shooter!
It's not just Gander, I was at a local gunshop yesterday looking at a Sig 227 and I asked the guy if Hogue made a rubber grip for it, he told me that sometimes they come with additional backstraps in the box , and that I could buy Hogue or some other brand rubber grips online for that gun.