No idea how to find a good PM. The problem as I see it is there are too many variables to quantify in an interview. Even if they answer your questions correctly there are still a million things they can do wrong. How are you going to quantify things like: how long for you to respond to my emails/questions?, how many mistakes are you going to make?, how do you I know you're using quality/honest contractors?, how do I know you're going to pay attention to detail?, how do I know you're going to put time into finding a quality tenant?
My experience is that you don't know the answers to these questions until you've been with them for awhile. My view of PMs is that owners don't pay them much, so why would they put alot of time and effort into your property? I've hired 3 PM companies to date; the first two were horrible and I fired them, the 3rd is newer and still in the "we'll see" phase. If this one doesn't work out I'm done with PM and will just start burying jars of $ in the desert or something.