But if you're buying used to get a serious discount, your best bet is probably to buy locally on Craig's List (if you're in the US), or something equivalent. Of the 5 Macs I've had, four were new and one was bought used on Craig's List (for about half of what it was going for on the refurb store, even though it was in mint condition and came with AC+), and they've all been great. The way to do it is to tell the seller you're serious, negotiate a price on the phone (so the seller knows they're not wasting their time), and tell them you'll need about 20 minutes to do an inspection and run some tests (you'll want to download the aftermarket apps they mention onto a USB stick):