Wiping An Apple Mac For Resale
If you've erased the drive, you're most of the way there. It really depends on what you want the experience for the buyer to be. I would print out this web page and check mark what you did so the buyer's mind and yours are both at ease:

"What to do before selling or giving away your Mac" - 
https://support.apple.com/en-us/HT201065

The last step (6 of 6) reads:


  After you reformat your hard drive and reinstall OS X, the computer restarts to a Welcome screen and asks you to choose a country or region. If you want to leave the Mac in an out-of-box state, don't continue with the setup of your system. Instead, press Command-Q to shut down the Mac. When the new owner turns on the Mac, the Setup Assistant will guide them through the setup process.


If your Mac doesn't come with Internet Recovery, you might consider making a USB drive for them to install the version of OS you want to ship. They can always call AppleCare and arrange for replacement media or a download code to redeem the version of OS that shipped with the Mac in question. Most recent hardware works with Internet Recovery and most older hardware has physical install media you can/should ship with the hardware or that could be ordered for nominal cost from Apple.