Sounds very dodgy, I'd tell the buyer that you're only prepared to ship to the account address and put the onus on them to prove their bonafide.
The problem that you have with an international sale is that the force of law is week to non-existant: If you're not happy, don't ship. The buyer could say that he's accepted a contractual arrangement with you, but between the UK, the US and Vietnam, he's going to have trouble pursuing litigation.
At £450 it's worth him making arrangements, if it's dodgy he'll disappear!