It might be safer to have a 2 year min rental history.  

I didn't have to; I was an excellent prospect with a good job, good credit, and a solid history.  

The first thing I would do is to check the listing history to see if it has fallen out of escrow multiple times.  

Definitely deciding based on rent record/credit history is best move. 

My family friend agent told me Realtor.com is as close as you can get to the MLS.I use SOLD history in an area to estimate the comps (realtor) and use zillow to estimate rentals in the area.

The owner of the 4 plex says it has good rental history.

@Alma MillsAs long as the applicant has stable job history, verifiable income, and good credit, I think you'll be fine - especially at this price point.Most of LA is paying the highest % of their income on rent compared to other Americans.Renter Households Paying More Than 30 Percent of Household Income Towards Los Angeles Has the Most People Paying an Insane Amount of Their Income Toward Housing

The commercial brokers will first shop the good deals to buyers they know w/ a demonstrated history of closing on their offers.  

Check for criminal history at least!

If no one can pay it off, I assume it will be on the seller's credit history?