the maintenance comes in three levels.
Low, medium, and high.
If you are currently in 1 or 2 stars it's okay to hire low levels.
But at higher levels I would have really recommended to hire medium, and if your achievement goal is to have 5 stars hotel you should hire the high one.
Just click the hire button after typing in how may you would hire on what level (you can't only hire 3 max. overall) and it wouldn't tell you either the hiring works or not. But you will know from the resort review the next day.