I'm not an avid mine craft player but I feel like playing a bit. A few questions:
Can the account be used to play minecraft anywhere in the world?
What steps need to be taken to ensure you wouldn't regain access to the account once (if) I buy it.
I can answer for OP
Yes it can be played anywhere in the world
You can change the email address of the account and the password of the account to not give him access.