Budrew wrote:
Sure, but I would imagine that it will be common for people to sell their Macs with upgraded OSs.
That was only OK when you bought the Upgrade DVD and included both the original system discs and the disc you used to upgrade the OS.
Since Apple has now gone to the Download only model of OS X you now always need to install the Original OS or an Upgraded version that you have the DVD disc for.
If a Mac came with Leopard and you upgraded to Snow Leopard and then to Lion or Mt Lion you must remove Lion or Mt Lion and reinstall either Leopard or Snow Leopard and include all the discs for that system, Originals and the Upgrde Snow Leopard DVD.
If your system came Snow Leopard and you installed Lion or Mt Lion thenn again you remoeve Lion or Mt Lion and reinstall Snow Leopard and include the original discs that came with the system
If your system came with Lion and you upgraded to Mt Lion then you remove Mt Lion and reinstall Lion.
The reason for all of that is because with the Download only OS all upgrades are TIED to YOUR Apple ID, not to the computer. So the new owner can not reinstall Lion or Mt Lion, whichever you upgraded to, without using your Apple ID.