We do a quick 5 minute-8 question telephone screening that weeds out most of the undesirables and gives me valuable information.

We bought a undesirable commercial lot, rezoned it to residential,  and we can put 10 units on the lot.

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. 

I like the way you think as far as the type of areas you're looking in, it'll reduce your risk dramatically for undesirable renters making the investment much safer.

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.

Evicted undesirables in one side of the unit and re-rented.    

With respect to the law of building codes, permitting and contractors, I have to be frank--in Ohio, it is nothing more than a hidden tax, a protective tariff, and a way for the municipality to veto any development or renovation that its architectural review board subjectively considers "undesirable."