I just sold my 2011 MBA on eBay and am running into a small issue. My machine was upgraded to Mavericks which is obviously linked to my Apple ID. I know how to reformat the machine and erase the HD but when I go to reinstall OSX for a the buyer, I am asked to authenticate with my Apple ID. How can I reformat so the new user can setup the machine like the day I bought it? Obviously the MBA doesn't come with recovery disks so I am not sure what do do. Any help would be appreciated.