Jon, excellent points but I still believe that it is possible to rely on your team members to walk that area and take notes of "a number of run-down, empty houses with boarded up windows and yards overrun with weeds."
My property manager does just that for me, has noted an area with those items you spoke about and thus, we went elswhere. Since I send so much business to my PM, she would be foolish to give me incomplete or wrong info on items of importance to my research. She would stand to lose a great deal. There must be some amount of trust given to team members, although an investor should always keep close tabs.
Also good points Typrider. To be clear, I do not have low income properties (except one) as they do not fit within my investing model. This is not to say that you should not invest in them, many others do quite well with them. For me, and most of my investors, prefer newer, higher end rentals for a multitude of reasons. I have many duplex and 4-plex units (residential multifamily) and using a PM for them has been great. If a PM can manage an apartment building to the investor's satisfaction, there is no reason why they can not do the same on the smaller multi's.
Just my opinion and strategy I use.