I had a vacancy at one apartment, that usually fills easily, for a month and a half, another vacant apartment that needs to be renovated (but been busy putting out the rest of the literal and figurative fires), a porch roof at one property that the joists collapsed due to our snow last year and is now leaking into the foyer of the first for apartment and the contractor who was supposed to do the work refused to put my company on his insurance policy as an additional interest, so I am back at square one looking for contractors, a tenant's unauthorized long term guest caught another porch on fire when he carelessly threw his cigarette butt next to the building (in a non-smoking building), crossing fingers my public adjuster will get enough money from the insurance company to fixed everything, gave the tenant of the long term unauthorized guest 30 days notice, but have a feeling she won't leave which will turn into an eviction which will make the process last another 45 days on top of the 30 day notice (there are reasons I did not do the eviction first and am going with the lease termination notice), and received notice that another tenant is terminating their lease 5 months early and will be gone in a week.  

I am under contract on a unit and when I went in for the inspection, the current tenant was sitting on the couch smoking cigarettes inside, as if he has been doing it for years.My question is, in trying to determine if I should buy this unit or not, how hard is removing smoke odor from a unit; meaning the carpet, paint. etc.

I've had two occasions where the reference they listed told me not to rent to them because they were violent, late payers, or too needy.Not doing a criminal, credit, background check, which might have revealed criminal or credit problemsBeing slow to evict (mentioned by others)Believing their sob storiesAccepting partial paymentsFailing to document every conversation or interactionNot walking through the property to make sure they're taking care of it (I now walk through every 9 months so I can see problems in different seasons)We've found crack pipes and other paraphernalia after they moved outWe've discovered piles and piles of trash (some bagged, some not) in closets, basements, sheds when trash cans and pickup service are included in their rent - all they had to do was carry it out, at no cost to themWe've Found smokers, pets, extra peopleOverall, I've had great success as a property investor. 

If someone’s qualifications on the app don’t meet your requirements (income not high enough, smoker, pets in a no pet rental, desired move in date doesn’t line up with when you want the unit filled etc) why would you waste time on a background check?  

Cigarette burns in carpet in bedroom4.

My grading contractor will gently dig up the tank, and one of my workers wants to keep the tank to turn it into a smoker/grill.  

Hopefully, they're a smoker with an insensitive hooter.6) Paid a guy to remove all ceiling acoustic and reprinted with oil-based Kilz primer.

A poster here already mentioned about the stuff people waste their money on: booze, cigarettes, lottery tickets. 

see this smoker/BBQ?

We smelled cigarette and weed smoke on the first night despite our clear no smoking indoors/no illegal drugs rule, and our messages asking them to please refrain from smoking indoors had gone unanswered.