Your CS9 appears to be from the "early" production stainless series, as it lacks an ambi safety/decock lever ... although someone could've just as easily have decided they didn't like the "wide" ambi, and had one of the earlier single-sided parts installed ... and the sights appear to be after-market night sights.
These are terrific little guns, and the price seems to be a very good bargain, if everything checks out normal ...
Check out the S&W forum at:
http://www.smith-wessonforum.com/cgi-bin/sandwcgi/Ultimate.cgi?action=intro&BypassCookie=true
Search for CS9 related threads under the Pistol section, and you should find quite a bit of info about your new pistol.
I've only got a bit over 1,000 rounds through mine, as it's still fairly new ... Mine has exhibited excellent reliability and accuracy with a decent range of ammunition so far ... 115gr JHP, 147gr JHP, 115gr +P+ JHP, 124gr +P JHP, 127gr +P+ ...
The only internal change of which I'm aware is the plunger of the recoil guide rod. It was plastic on the early pistols, and it's polished stainless nowadays. This isn't a big deal, although the early plastic ones could get a bit scratched up with a lot of disassembly/reassembly in some cases. This is an easy-to-change part yourself, assuming you ever need to do so ... as it simply snaps out & into the recessed spring of the CS design guide rod.