I was thinking that the assessed value might help weed out the very undesirable properties/areas, though I haven't really looked into the assessed values of the properties in the rougher areas.

Military housing is at high occupancy on-post, making various home displacements more common off-post in hotels or short term rental homes.Small multi-family homes vary in neighborhood types, but the majority of them (but not all) are in a low to middle class area, raising the chances of getting unappreciative or undesirable tenants.As I mentioned earlier, I have no properties and only watch the market for now.

Examples of pitfalls include purchasing in an undesirable area, not understanding the market values (vs. list prices), not knowing the rental values (current and market), inheriting bad tenants, buying a lemon, going rogue on renting and management with no contacts / systems / no legal understanding of PA and Municipal landlord-tenant laws, not having trusted resources and contractors in place, using out of state lenders or shaky financing, throwing lipstick on a pig when renovating a house and wondering why it's ARV isn't increasing, tenants are renting, etc.

If something happens and makes the closing either impossible or undesirable, you lose whatever time and money you've put into that property.Worse, if damage or loss to the property can somehow be traced back to work you or your contractors did, guess who is getting sued. 

You were made aware of undesirable conditions and made immediate attempts to address the problem through a capitol improvement not just a simple repair.

Do not spend time trying to turn an undesirable suspect into a client; spend time FINDING those who need your expertise and product, and are willing to PAY your desired price5.

The "undesirable for incorporation" comment in the wikipedia article is likely to change in the next decade or so IMO.  

When I hear about a situation or action which I find undesirable I think Yuck.

It's those areas that will have lots of cash buyers.That being said, unless you work an area that is really remote, really undesirable or really high end, you are not going have a problem finding cash buyers in this market.

Dont trust anyone or you will end up holding a undesirable property.