I figured as much. That seems absurd, and I was almost in shock when the salesman told me that. His exact quote was "I can't sell you the car cash because of exporting reasons. You would have to finance at least half. To pay cash you have to be a local resident and even they have to jump through hoops".
It's amazing to me that someone would pull this on a $130K transaction. This is my first Mercedes purchase, and so far my introduction to the world of Mercedes dealers isn't going well. I understand that they want to make as much profit as possible from the limited stock of the new S Class, but this isn't the way to do it. I had to look out of state because most of the S550's in inventory are not as well equipped as I would like. I guess I'll keep looking.
Anyway, thanks for confirming my suspicions.