I hear you about the dedicated graphics. Only that second tier of the 15" units has that. Also the unit he's selling was bought as you know, just before the doubling of memory to 16GB and the .2Ghz processor speed bump; and there's a remote chance, that's the reason why he's selling it. If he's willing to give you the serial# (a positive sign), maybe Apple could be of some assistance?
Here's a list of some recently stolen laptops (as well as some other computing electronics).
If he won't give you the serial#, I'd say run! If, on the other hand, everything is on the up-and-up, the $1300, even tacking on AppleCare, is still a pretty good price for that barely 3 mos old laptop. Tread lightly, and go with your gut!