I would like to offer the best "relational" way to handle this situation - which only supplements and doesn't substitute for Nathan's approach.First, have the persons you are buying property from notify tenants of change in ownership as soon as offer is accepted. 

Substitution of Collateral – if you ever sell the property and you want more cash - DON’T pay off the mortgage – substitution of collateral clause in what will work.

Its simple, but tedious, but there's been no substitute for the quality of leads/lists in my experience.  

No substitute for studying, but a good place to start. 

There's no substitute for experience.Folks bop around from market to market thinking they can be successful. 

The following article presents basic facts and features of the contract for deed and offers suggestions for minimizing the risks associated with this mortgage substitute.

Then it can be well over a year before you get a steady stream of clients to substitute a portion of your w2 job. 

But I also know that if an area is appreciating in home prices you would be able to accept a lower cap rate since you're substituting the appreciation of the house and if an area isn't appreciating at a fast pace then it would make sense to accept a higher cap in substitution of a slower appreciating market. 

There's no substitute for walking/driving around to figure out what might be a real up and coming area and what has had better days. 

CODE CH. 5-12-110(f)}• If, contrary to the lease, an essential service is not provided, or if the landlord fails to maintain the building in material compliance with the Code to such an extent that such failure constitutes an immediate danger to the health and safety of the tenant, and the tenant or tenant’s family or guests are not responsible for such failure, after giving written notice, the tenant may do ONE of the following:1)Procure substitute service, and upon presenting paid receipts to the landlord, deduct the cost from the rent; OR2)File suit against the landlord and recover damages based on the reduced value of the dwelling unit; OR3)Procure substitute housing and be excused from paying rent for that period.