Buying Iphones Used - What tests should I demand?

I've been looking at getting an iphone 3gs used (yeah, I'm cheap).

Just wondering, if I buy used from a local classified or Craig's List, what should I ask the seller to demonstrate?

-That it makes calls
-That it will synch
-That the cameras will take pictures
-That it will connect via bluetooth, and to apple's App Store

What else?
Or what are good methods to test these things and other important things?

Thanks,

basically if it turns on your probably good. What breaks the easiest on an iphone is the screen from being dropped. They also are really easy to repair, so maybe buying one that has a broken screen is an option? Ive fixed a couple friends of mine who have broken the glass/lcd/digitizer (touch) layer and its a simple ebay order and swap out.