It's really not a viable market, IMO, shoot for nicer homes, while that may be slower to grow it will be steady and real estate is a long term game.

Yes it can be come a hazard and health and safety issue and a code compliance issue if city cites you for a problem issue, or someone is allergic gets bitten and needs medical attention, maybe a bigger issue. 

If you have to move for work or medical reasons at less than 2 years residency then you can prorate the gain for the time you lived there.  

The market has cooled a bit and we're into the slower months2.

Typical reasons are loss of job, reduced income from job or business, divorce, death in family, health issues affecting employment, overuse of credit cards, medical bills. 

Scenarios that easily come to mind:  1) owner moved to nursing home (Nursing home not attaching the house to recoup nursing home costs); 2) owners stopped making payments due to [job loss, sickness, medical bills,....] with hopes of starting back, but time runs out and not enough energy to list house. 

That's great to supplement income, but in terms of buying more rentals that's a bit of a slower plan.

-month-to-month leases with pre-approved sub-leases over the summeror you can target the quiet/too busy students (law, medical, international merit awards, doctorates)

Even in the slower time like now, you're limiting your chances of being able to get under contract if you wait to talk to a lender after you've already found it.

I did not need to be unemployed to find investment opportunities or to manage my investments.I had the best of both worlds, retired early at age 56 with 35 years service a pension and medical coverage.