PatrickGSR94 :
Would formatting and re-installing the OS not be sufficient?
If you are confident the buyer is not someone after your personal data and you intend to include the OS in the purchase, you can do that. If this is for eBay or you don't know the buyer well, or at all, I'd suggest wiping the drive a few times first and go from there.
It's just a little more work to protect yourself from potential damage later on.
fowang :
My method is using a tool called the FORMAT HAMMER lol
That's a very effective method but it also effectively renders the drive unsellable.