I use a similar method to what Bruce uses to eliminate undesirable properties then I drive by anything I might bid on and put my eyes on each and every property.

I've seen gentrification spread right up to a block of S8 buildings, and then go around that block leaving it right where it was and will probably always be (undesirable). 

Typically there is a one or two year ramp up period where you get all the deferred maintenance and/or undesirable tenants out.

Meaning, if you own a larger portfolio and 1 property is experiencing undesired returns.

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.

Originally posted by @Michael Bracken:Some people would be surprised at how effective a $25.00 application fee is at weeding out undesirables.

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. 

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.