So you sold your mac on eBay, good job!

But now you want to clean it up and prepare it for the new buyer, but… maybe you don’t have the setup discs to do a clean install? Maybe you want to apply the latest software updates because you’re nice or something, but not leave a user-account sat cluttering up the mac for the new owner.

Have no fear!

First, boot to single-user-mode by powering up your computer while holding down the Apple and S keys.

Then, as it suggests, run /sbin/fsck -y and /sbin/mount -uw /

Now for the hard part!

Remove the user account(s) from the OS’s database:
nicl -raw /var/db/netinfo/local.nidb -delete /users/[user-name]

Then delete the actual folder with:
rm -r /Users/[user-name]

And then tell the mac that it’s never been set up:
rm /var/db/.AppleSetupDone