Before the internet, I sold a boat to a guy in Aberdeen (I was in Wales). He saw a tiny pic in Autotrader, rang me, told me he'd have it and would send a courier to get it.
A few days later, courier turns up, gives me a wad of cash, hooks trailer up to his van and clears off.
Not the same I know, but I never thought anyone in their right mind would ever buy something like a boat (or a car etc) without seeing it!
Having said that, what you've received is a scam attempt, and there's always one way around it. Cash on collection ONLY please.