For safety's sake, definitely an Apple refurb. eBay, Craiglist, etc. all tend to be a crap-shoot, even with high feedback sellers. But then again, there's plenty good to be had on eBay - I've purchased several used computers on eBay over the years (both Apple and other PC brands) and only had one real issue; and that issue was handled to my liking by the seller. I've also sold ALL of Macs from the past on eBay, including G3/G4 towers, a G4 iMac, a 17" white iMac, a Core Duo Mac Mini, a PowerBook, a Macbook, and two Macbook Pros. Point is there are good, honest sellers (ME!!!
) and plenty that aren't.
My advice: If an Apple refurb is out of your price range and you need a new(er) Mac, eBay is definitely worth a look-see. Just do your research and practice safe buying.