I am looking forward to the conclusion of this thread. As I live in Wisconsin, very near the Minnesota border, I lurk Craigslist looking at instruments--occasionally finding entry-middle level ukuleles at good prices. My goal is to eventually make it to Hawaii and to buy a K model while there (sure, you could order one, but it seems better to buy one in person). I was listening to the Ukulele Site's podcast, and I'm interested in the new KoAloha Opio tenors, which are 1/3 the price of their Hawaiian made brethren.
Anyway, this is a fascinating story. It makes you wonder about the history of the instrument. If a "player" purchased it, it would have newer strings on it. Perhaps the original purchaser became ill, or passed away (I hope not). Or maybe it was purchased by someone with a lot of extra funds that doesn't really care about the price.
My guess is that if they are willing to sell for $500, you can walk away with it for $450. I've simply been e-mailing offers to people on Craigslist and letting them respond (My best offer is going to be $X, and I still need to see it). That saves a lot of time and stress in the transaction on both sides. I even did that for a recent car purchase with a dealer. It sure helps to be able to do price comparisons on the web before making a decision.
If you get it--send pictures and tell us more about the history of the instrument.