Little things like trash not cleaned up, yards not mowed, paint deteriorating, vandalism, trends in list prices.

Seems like they could actually drop if people walk away, buyers know about these defects, houses deteriorate more, mold issues settle in, etc.

I would definitely look for some of the main issues that are found in old homes such as foundation issues, old plumbing (rusted or deteriorated), electrical (I believe that age will have fuses instead of breaker box (not an expert in this arena), and other deferred maintenance.

And this is what I found:- He is 73 and in deteriorating health.- He is willing and motivated to sell.

It is a side by side duplex with a ancillary unit (converted garage into a single family) and after running through it with my home inspector and contractor, it's looking like I'm going to need to put $40k into it in just safety upgrades (3 unfit falling over porches, deteriorated window sills, smoke alarms, second means of egress).

To give some perspective on the comment from @Josh Caldwell:If you visited the Port Richmond area of Philadelphia, then you probably had a chance to see some parts of Kensington as well - where due to drug use there are parts of that neighborhood that have deteriorated to the point of being close to fitting the "war zone" description; and that neighborhood is more racially diverse than how you had described your take on "war zone".

I do however feel as though the situation has deteriorated to a point where even a novice like myself knows enough to safely say that decisive action is long past due .

Except it is already cracking and deteriorating from the sun. 

Your houses will continue to deteriorate, and you'll just find the next sucker, b/c I get it-- there's a market, there's a lot of demand from the desperate people who no one else will rent to.      

Some of the pipes had almost completely deteriorated in a fellow investors rehab property.