Well, there's a new one on Gunbroker on which the bid is at $601 ("reserve not met"), so I guess it's up to you.
My 520 cylinder definitely has residue on the exposed titanium, and, so far as I can remember, it's been there since I first fired it. If the cylinder is really clean, chances are it hasn't been used much, if any.
Think about what you want the gun for.
If it's a utility gun, like mine, and you want to shoot a fair amount of .357s through it without worry, then the 520 Ti 7-shot is a fine gun.
If you want something a little spiffier, with nice blueing, will shoot mostly .38 Specials, and never will shoot "hot" lighter weight .357s (which can cause forcing cone problems), get yourself a nice Model 19. I happen to think the M 19 is the most graceful gun S&W ever made, but neither my wife nor my budget will allow me to stock up on them!