Usually a warranty is for the original owner only.
The size of bike you take depends on your proportions. I'm 5'6", so a bit over average for a woman... and I'm proportioned so I take a small bike, like 50-52 cm. It's just as likely that someone my size would take a bigger frame - only way to tell is measure and test.
Bikes often go for more than MSRP, so he might not be lying about the price. On the other hand... I know Jamis bikes mostly went *up* in price from 2007 to 2008, usually by $50-100. So he's claiming he paid at least $100, maybe $200 over MSRP. That's a lot when the bike is pretty inexpensive.