I've bought several used laptops on eBay, old ones for playing DOS games and the like and had no problems but I don't think I would take the risk of a new computer via that route. If you decide to do it here are the rules I follow when looking for stuff like that.
Be sure the seller has a LOT of positive feedback, few or no negatives, and make sure the negatives (if any) he does have are not of the "Computer came DOA" variety. Also do not buy one as is ever. "I have not tried it" or something similar is just another way of saying it doesn't work. Make sure they give a guarantee.
