Bryan,
I agree that many management companies out in this world today are wanting that turn over as that is where they make the most $. With that being said, you'll also find companies (such as the one I work for) that are honest people, we turn down many applicants that pose a potential threat based on the rental history. Our main focus (and should be everyones) is tenant retention. The broker is an investor himself so it helps to have the same experience as the client you are working with. Of course, you can screen a tenant thoroughly and still end up with problems such as eviction, collection, damage etc.
I would suggest anyone looking for a property manager, to do a lot of research on the company before signing a contract. I could post a whole new thread about the horrors of a bad property management company, as I have had the unfortunate opportunity to work for a few in the past.
Ultimately, a large deciding factor is the area of the property for which you manage. It isn't to say that a bad neighborhood will ALWAYS bring a BAD tenant; but rather the process could take longer to find the most qualified tenant for that area, which again could cost you money by having your property sit vacant longer. Not to mention the lack of care I've seen people put into renting a property in a less desirable area.
I am just seeing the investment isn't always as great as it seems in the long run.