I'm currently in the market for buying a 250 myself and this is a guide that I found that has a lot of good general information about bikes.
http://www.clarity.net/~adam/buying-bike.html
It has a section about quizzing the owner, and it also tells you a lot of information on how to inspect a motorcycle in general before purchasing it.
There is a lot of information out there so don't get the wool pulled over your eyes
Also here in Virginia a week ago I was up to the dealer and one of the guys said that this month Kawi has a deal going on and they were selling the black and red bikes for 3700 + Dealer fee + Tags/tag/titles for a total of about 4300. The green bikes are not part of this months deal for them.
I've found a couple used 2011 around here that were apparently dropped at 5 mph practicing u-turns lol. If you feel like you are confident enough to look at a bike that was dropped; then you might be able to get one as low as 2700. Obviously the East coast is cheaper then West Coast it seems.