Securing purchased Gmail fully

[Man of steel]

How can i secure a gmail account/google ID when i buy it from someone? many games are linked to google ID and its easily revoke-able. i need tips to secure it.

 

[doomedtofail]

2 factor authentication and once your computer is recognized as a known device remove their original phone number from account. Make sure no back up email is tied to account. Check login history make sure theres not a pattern of different locations logging in. Close all login sessions that are not you.
There is no 100% way of securing it. As is true with most accounts and games.