It sounds like a scam to me too.

He has paid me a total of £500, and that is currently in my PayPal account. I charged him £50 for shipping via FedEx to Vietnam with extra insurance. I am thinking this is a hacked eBay and PayPal account or something and the guy in the US has no idea and will issue a chargeback as soon as he finds out. Leaving me with a lens half way around the world and down £500.

I have told him I need to verify the sale over the phone, and I want to speak to him on the number on the PayPal account first. Lets see how far he runs away from this now....

Cheers

Cris.