There had a massive increase in fraudulent orders from Vietnam recently. We now get 3 to 4 such orders a day.
There is a 99.9% chance that this order is fraudulent. I would deny it unless it were issued by a Vietnamese bank and that the billing address matches the shipping address. (That is if your credit card processor can check this out for you you)
If you're gonna drop it anyway, might as well send a reply eMail that due to insurance company or bank regulations or whatever (good cop.bad cop) you regret to inform them that you can only accept cash instruments such as wire transfers or money orders by postal mail, for orders from Vietnam. At least you might catch a real one once a year, and that might pay for your lunch or a new pair of jeans on occasion. :o)