i came across a craiglist listing for an iMac 21" 2010 model w/ 4GB RAM, 1 TB HDD, i3 CPU. no other info given other than that he says he has the box and shows it w/ box in a pic on the ad. He is asking $610 for it. Seems too good to be true. What should I ask in an email and look for if I visit him and sit in front of it. Any diagnostics I can run if he lets me sit at it?