You should develop a hand-over plan. Once hired, the new admin and you should agree upon certain aspects of the plan.
1. A very thorough background check should be performed. The further back, the better.
2. During the vetting process make sure more people than you interview the candidates. Trust your qualified team members, even if pulled from the user pool.
3. Once hired and on-boarded, turn the keys to the kingdom over to the admin. That is why you hired him/her, to replace you as IT Mgr. An untrusted IT Mgr. is worthless.
4. You and the admin should agree a timeline and certain milestones, upon which you relinquish certain responsibilities at that milestone. Unless the admin proves subpar, at which point you start looking for a new admin. For instance, at 30 days in, you step back and turn all acct mgt. over to the new admin, totally. I suggest the whole timeline take no more than 6 months, and if you can develop a quicker one, the better.
5. Develop a root password mgt. system. Every time the root password is changed, it is locked in a restricted access safe. And, SUDO is always used.