Is this a typo, or does this seller really think that 8GB of 1066MHz DDR3 is worth £500 because it came out of a Mac? If that's really the case, I need to buy me a mac and put some stuff in it, and then sell it for hundreds more than it's actually worth.
tbh he probably checked the apple system configurator and looked at how much it cost to upgrade to 4gb then multiplied by two. I would hope it doesn't come to as much as £500 but... you never know with Apple (nb I realize most system buildings from branded companies have stupid upgrade prices )