That teaches the occupants that they aren't 100% responsible for cleaning up after themselves.

Only if you consider working every night, weekend, holiday, and times when I should have been on vacation lucky, mucking around in crawlspaces, hunting down houses, falling through floors, etc. 

It's middle class, low crime, clean & zoned in one of the top desirable High schools. 

Also the majority of those costs to covnert to a 2nd unit will need to be capitalized and depreciated, but some things (new appliances, flooring, paint, kitchen cabinets) can be shorter year assets vs. across the full 27.5 and IF it turns out that unit is > 50% you can use bonus as well on those items.

So bottom line they got away with it and are living in a beautiful safe clean country. 

Every 15 yrs HVAC, every 20 roof/kitchen/bath, every 5 flooring...  

Spending more than 100 hours and more than anyone else, or substantially all the time in the business.So if you own an STR and meet the test, you can set up a tax deduction machine.Some issues -- You have to count your time, and the time other people work in the biz (cleaning, maintenance, etc..)- If use the property more than 15 days or 10% of the time it becomes a residenceI suspect this is part of why the STR trend has picked up so greatly amongst professionals working in tech.

Never had an issue in 5 years of this when tenants have moved out I just send my house cleaner in for a deep clean NO turn over costs other than that.

We then cleaned all of the mold and reinsulated the attic.

She was paying on time and left the place clean.