why is it so freikin difficult to wipe a Mac and re-install the OS? I'm having a huge issue with a 2010 iMac I want to resell, so I wiped the disk using macOS Utilities. Of course I don't have the original (if I ever did)
You can not sell it with a later macOS that is tied to your Apple ID. You must erase and install an OS X version that the new owner can upgrade using their own Apple ID.
That is the problem.
You need to use the original OS X Install Disc Set that came with that iMac.
To make things a little easier, you can also use a Retail Snow Leopard Upgrade DVD or Lion Upgrade FlashDrive.
Then you can re-install the OS X and pass the Install media along to the new owner.
The version I had running on this iMac was High Sierra (2017) so I don't know if I can even go back to the original Snow Leopard version.
Mac software re-installation issues
