You will need deep pockets to supplement your tenants rent.

Agree totally with @Matt K....this is the first really good advice I've seen on this site in a long time...Foremost, markets exist in many forms and no two are the same (even in the same neighborhood)...if you're buying duplexes then looking at Marcus & Millichap reports is a waste of time...and CAP is simply an estimate of what investors are willing to settle for...would knowing that your target area is only producing a 4 CAP alter your marketing to sellers as you work on your next acquisition of a deep discount deal...perhaps on a purchase money mortgage or lease option?...

Becoming an appraiser sounds like a great way to really get a deep understanding for the industry.

You have to be born in a very, very deep part of the gene pool and live right for many years.

Dig deep enough to find out why the rent is where it is.

I get an awful lot of calls from people who say they are interested in getting involved in the note business, but then in the same breath they ask me "How quickly can I make money?"

Once you live and breathe this market everyday, you can spot the opportunity miles away. 

I am thinking thats the surest way for you to answer the above. my other question does not relate to licensure.. but how deep is this potential market.. does this stuff actaully exist in real life or real world.. or is it possible its a ton of time and effort for very little money ??? 

I believe there is a deep shortage of apartments in LA County, in some of the sub-markets. 

That doesn't work and will also freeze up their (and potentially your) sewer lines during extended deep freezes.