If it's a brand new in box but $500 off compared to a new one, it sounds really shady since I can't think of any reason to buy a laptop, let it sit past the return period without opening it and then sell at a huge discount...
Hey... sometimes **** just happens. I still haven't talked to any of these guys, as they dont seem to understand how Email works (you have to actually return messages to sell stuff), but the ads themselves are generally fairly vague. One guy sent a broken one to Apple, and got a replacement in return, but bought a much cheaper PC in the meantime and just wants the wad of cash. It was still within the return period (before it sold... and it sold immediately). Another guy says he bought it and decided he just doesn't need the power. Another said it was a gift, but the wrong model. Thats what they say... so who knows. They cant ALL be lying. At least you can physically visit these guys, see the thing, see the receipt, even check it against ID's and dates if you want. Thats FAR more than anyone on Ebay or Amazon offers.
Further... while $500 is absolutely HUGE to me... Like, I might see $500 in one place maybe 2, 3 times a YEAR. To others, its nothing. I know people who spend that at the bar in one night, twice a week. Every week. I know guys who buy $2000 couches, use them 3 months and then give them away. Others that spend $100 on take-out per day... every day. One blows 2K in the casino and laughs it off. Some people just literally wipe their ass with money. Some others just buy stuff for the status... and Macs definitely fall within that area.