As a manager, trust me it sucks to have empty units. We feel the pressure. The truth is that sometimes landlords are a little unrealistic about market rent or time of year (cold weather slows down leasing a lot).
My standard answer to clients is along the lines of: "I can fill it tomorrow if you lower the rent or lower the leasing guidelines. This is just an equilibrium situation. We can change certain aspects of the equation (rent amount), and others will change with it (vacancy rate)."
Then we show them that it's listed on every site in existence, and we show them all the leads we rejected, etc. I think just letting them know that we are really on top of it helps. Another thing we do is not take on ugly, broken, or infested units. We just tell clients that we cannot list any unit that is not rent-ready.
A bonus to fill it quickly wouldn't change our work ethic. We are full-go from the first instant, the first phone call. We are never not full-go.