I bought a used mac on ebay a few months ago- power seller, bought a one year warranty- 100% positive on 1000's of feedbacks- it's a great little refurb machine- I could tell by the descriptions,warranty policy,etc that this isn't a scam.
Came with all proper software installed- we could see aftermarket keyboard,etc installed(ds knows these things) but it works just like it should,and seller has a 30 return policy if it isn;t operational.
less than 300.00 and I'd do it again. But this is the only buyer I'd buy from, I don;t usually buy stuff like that from ebay-