The Craigslist scam in my area was $1200 for an 820! The email response usually makes it pretty darn clear if it is a scam. On the ones I have seen recently, the seller has suddenly had to move across county for work and the new employer is providing a new computer - nope, the idiots can't even keep the scam straight, lol.
Close to half price may possibly be genuine, but be careful. In addition to my CV, I got a similar deal on a Sailrite LS-1.