Technical Question #3 at interview : "Briefly explain the Filesystem Hierarchy Standard (FHS)."
If they can't answer that, or demonstrate the ability to say "I'm sorry, I don't know", then they are not 'Admin' material and should ONLY be dumped in group 'Users' until CPD takes effect and they can be trusted.
Same sort deal goes for prospective Windows admins...if they can't explain %APPDATA%...