Kensterfly
You are right that the shipping FFL has no obligation to hold the money until you (or your receiving FFL) receive/inspect/approve the weapon. In fact, most probably would turn over the money the moment the gun is received for shipment. As a seller, I would never agree to turn over my gun (even to a FFL dealer I trust), and wait for payment. If you order from any online dealer, they require payment first - then they ship to your FFL.
IMHO, it seems that you're stressing a lot about this "deal." Unless it is some sort of super-fantastic, once-in-a-lifetime bargain, I think I'd just walk away.
One final thought about armslist: I've sold about half-a-dozen guns on armslist, and never had a problem. However, I've always insisted on face-to-face transactions. Even at that, I've always worried that I might be selling to someone who might not be legally allowed to own a firearm. And I know this may be hypocritical, but I won't buy a firearm on armslist unless the seller has documentation to prove he/she is the legal owner.