I would also take a look at alcohol and cigarette company profits  during a recession, as they actually go up, not down.

Considerations I've found so far include: various layers of outdated insulation (mid-80's fiberglass stuff laid over old vermiculite), 1x2's nailed together to create 2x4's (but still relatively sound structure for the age), asbestos siding (needs a powerwashing and I've found it's totally OK, until it's time to rip it off or demoed), 1" galvanized metal water main is very old, electrical wiring that is visible is a hodge podge mess, there's an old gas pump on the site (not sure if tanks are still buried), real bad mold in bathroom, at least 3 layers to the foundation (that looks solid still), ugly old wallpaper, cigarette smoke smell, kitchen is a complete gut and remodel, nearly the whole home is.  

Before renting out a unit I have to make sure by asking if anyone smokes cigarettes, marijuana, hookah, etc.

Originally posted by @Michael Robbins:Whether a tenant has a barking dog, smoking cigarettes, smoking marijuana, etc...

You can rent machines that put out near lethal doses of ozone that use a timer that you set, vacate and then come back hours after the ozone disperses.We've used ozone to get rid of bed bugs, mold, smoke damage, cigarette & weed odors, etc.Recommend you Google how to get rid of meth contamination, so you understand the process and don't get ripped off!

Metal Building maybe $60k, he wanted to keep renting, he was running some sort of part time cigarette or E Cig business out of. 

They left the unit in very bad shape (holes in walls, cigarette smoke smell, soiling and damage from unauthorized pets, graffiti and intentional damage, unflushed turd and vomit in the toilet, drug paraphernalia and liquor bottles, disgusting furniture and trash left behind, fridge, dishwasher and oven looked like crime scenes, cockroaches in the cabinets, grease down the drain, literally the works).

The rental leach bed had tampons, baby wipes, cigarette butts, ear swabs, and of course rubbers clogging it.

People will spend bundles of money on cigarettes or other vices, but never draw a connection on how they never have enough money.People have money for things they want, but often feel broke for things they need.

@Ned J.I was able to tour the upstairs since it is separate and he doesn't live there. the down stairs needs a lot of work as in it looks like a dirty frat house (looked in through the windows) there is trash everywhere and the walls have years of cigarette smoke on them. the foundation looks good, HVAC too (was able to get into the basement since there is a exterior entrance. however the brother has convictions for "criminal property damage" so I guess my concern is him taking a bat to everything/ ripping out plumbing, and the numbers not working with 70K in damages.