Property Managers work for the Property Owner. Many times the tenants believe that the agent should work for them. Like so much of our world today Tenants seam to believe that the world owes them something. They don't pay rent, they are late with rent. They damage property, fight with neighbors, many other problems. But they do not believe that they should have to follow the rules. Or pay what they agreed to. When they get evicted its always the Management's fault.
That being said, not all management companies are the same. Many will try to cheat you or refuse to do repair work.
One of the really good ways is look at the property. What condition is it in? Did they show it to your dirty? Are they willing to let you do work on the property? Are they hard to reach by phone? ARe there office hours very limited? These can all be indicators that you need to move on to a more reputable company.
Ask around. People in the community usually know. You want a manger that is both touch and fair.