David,
Much depends upon the amount of Color Hardening left on the frame, and how well the Carbine presents beyond that.
Any and I mean ANY alteration screws the value of the gun. Watch for sanded wood and replaced sights.
I can tell you that Marlin 1936's do not sell as well as Winchesters from the same era, but then again any good, correct, unaltered Color Hardenend Winchester '92 or '94 (these are pretty rare) will bring 4 times that. Winchester generally didn't color harden frames after 1907. Marlin however, carried this finish / process much later.
If you like the gun and the $500 is replacable, it may not be a bad deal if you're looking for an investment. At least this gun is in .30-30. The .32 Specials are a real dog....
One thing I can tell you though is that the only thing rarer than a Collectible Marlin is a Marlin Collector with money.
Good Luck.
Nice Brookie this morning by the way.... I wonder if you're fishing up around my old stomping grounds of the Eastern Adirondacks.....
Good Luck with that Marlin.
Drew