I’ve seen some nasty houses for sale with ceilings collapsed and paint separated on every surface and walls crack over cheap people with pipe dreams of restoring grandmas old mill house leaving it cold in the winter .

Inventory from the collapse is way down. 

Roofs collapsing, HVAC systems dying, flooding, meth cooking on the property, etc.   

Otherwise, you can scope the line after its under contract and retrade if it has collapsed.

If you steal your tenants deposits and let the staircases collapse then yeah your going to lose and it won’t matter if you have a llc a c corp a s Corp or 10 trillion in umbrella insurance

Over time these holes will expand into small caverns, and can eventually collapse.

I’m about 40 years old, and do have a reasonable normal(salary) income of about $200K, but looking to hopefully semi-retire in a few years if I can, although need a few more sources of passive income as of right now.Disaster scenario in my head is… stock markets crash(loss of stock equity), along with the tech scene here in California collapse (loss of job/rental price decline or vacancies increase), and adding icing to the cake with perhaps some earthquake affecting my real estate here (we are long due for a big one).Feeling a bit paranoid but would rather intentionally decide what to do, whether to keep or to diversify. 

That list does cover the heavy hitters, but just to sum it up here are some that I always look for (I also get a home inspection for each property before buying it and ask my inspector to check for these things).Stuff You Can't See (aka takes a test or a professional)AsbestosLead based paintLead in the soilBuried oil tanks (if the home use to have an oil furnace)Collapsed/Rooted sewer linesPoor septic tanks (I have heard of people buying homes and finding out that a 50 gal drum is the septic tank)Stuff You Can See (or easily find out on your own)Old wiring (knob/tube, cloth, aluminum)Cast iron plumbingBroken roof raftersDry rot, termites, wet rot, and just wood support issuesMoldFuses/Multiple electric panelsSloping floorsCracked foundationsSigns of water in crawl space/basementThose are the ones just of the top of my head which can quickly add thousands of dollars to a job.

However, we're in a very unusual time where rates are artificially low and will likely remain that way until the overall economy collapses because even the slightest rate increase seems to show how weak our economy truly is. 

Example: If there is a bathroom located directly above, a toilet back or burst pipe could cause the ceiling to collapse from the weight of the water.