Just check it's functions, look at the status of the battery (Sol will indicate both if the transmitter battery is
low as well as permanently the status of the Sol battery.) If the Sol battery indicator shows just TWO bars or less, it MUST be replaced, THREE bars means replacement imminent within a less than 20 dives. Both are, as said above, easily replaced by yourself, they cost together around $25,- including the O-rings.
Screensaver (plastic cover) will cost you around $15,-
So try to get another $ 50,- to $100,- down on the price, as it is also two years old. (If not, it still seems a fair deal.)
By the way, does it have the newer software (1.5) installed? No problem if not, that's done through Smarttrak easily as well. ( If you wait another month, Trimix should finally become available, probably with an upgrade as well.) You can verify the claim of 45 dives by scroling through the log on the SOL or download them to a computer over IR through the gratis program Smarttrak. There are probably more "dives" on it, as each factory test shows up as "dive" as well; they are mostly test runs, not longer than 5-10 minutes or even shorter.
Anyway, SOL is IMHO a great computer with a lot of nice features, including the compass, which does not need to be held strictly horizontal in order to function! (no, I don't get paid for this).
(I got mine for 500 euros with transmitter, but had to buy a new heart belt for 25 euro. In Europe they go for between $750-850)
Hope this helps a bit.