I have to say here, it is so good to know that owners get as frustrated about incompetent property managers as tenants do.
I've never owned a property, and usually blamed the pm for things not getting done, but you do wonder weather or not they've passed info on sometimes & if the owner has chosen to ignore the problem.

I guess the most important things really are to ensure you have a lease agreement & a bond. Private renters often don't bother with a bond. Make sure you know and understand both your rights & the rights of the tenant.
And be confident. Know that if you need to terminate the agreement, or give a warning, for whatever reason that you can & will do it.

Don't rent to friends or family. My sister is renting from her partners boss & friend. Makes it so much harder when you're emotionally involved, for everyone.