We see the same thing in the Atlanta CL every week. The past week it's been a 5D for $600, two weeks ago it was a 5DMII for $1,700. Three weeks ago it was 40D for $700. The ads are usually very detailed, with accessories and specs (most likely a copy and paste).
I've actually replied to a few of them - just to play games with the scammer. The response is as stated above; called out of the country suddenly, but willing to ship via DHL or "Royal Mail Guaranteed Delivery". One other interesting response that looked real - a 40D w/grip posted for $500, but the reply came back announcing the "new" price of $1,300 - a classic bait and switch.
Bottom line - if it sound's too good to be true - chances are it is!