Same with Drywall, I know what good drywalling takes from having done my own, and choose to hang it myself, but hire professionals to mud and tape and do the skim coat. 

Some related reading for you, since you seem to not like research (an undesirable attribute in an agent, BTW):http://www.biggerpockets.com/forums/21/topics/170-how-to-find-a-good-realtor-http://www.biggerpockets.com/forums/21/topics/74296-what-defines-a-good-re-agenthttp://www.biggerpockets.com/forums/21/topics/69232-what-do-you-actually-look-for-when-selecting-an-agenthttp://www.biggerpockets.com/forums/311/topics/70483-how-to-find-a-good-re-agenthttp://www.biggerpockets.com/forums/21/topics/69807-value-of-using-an-real-estate-agent-in-the-deal

Those 20% are undesirable areas. 

It is undesirable and is a concern, but not as big a deal as it was in Northern California.

This is a difficult time to start out as a real estate investor IMHO because you can easily get stuck with an undesirable home.

Call MUD and play dumb and ask what the utility usage is for both the units. 

Unfortunately the bigger BP gets, the more trollers, the more scam artists and more Undesirable members will be joining our community, I wish that wasn't the case. 

In other words it’s clear as mud!

For example, North Philly by Temple University is a wonderful place to get into; however, the boarding neighborhood can be a little undesirable and breaking into the Temple market is difficult due to higher cost.

Undesirable size and floor plan.