I will be selling my early 2011 13" MBP that came Snow Leopard. I upgraded to Mountain Lion when it came out and installed it in my MBP. My questions is:
Do I have remove Mountain Lion and install Snow Leopard when I sell my MBP?
I always wondered this because Mountain Lion is tired to your iTunes account and if the person buying it wanted to do a fresh install, how would they do this?
As he/she'll have the Snow Leopard DVD anyways, I'd send it to the seller with Mountain Lion to save him/her the money for the upgrade. You can do a clean installation from the recovery partition.
make an agreement with the buyer. If the buyer wants ML, do a fresh install of ML. And being nice, as other poster had said, have a USB stick for her/him. If not, install the original OS what ships with the machine and hand over the installation media. I tought that was the common practice, a time ago. It is up to you to install the original OS only or update it.