I've taken several and they are a great supplement to a traditional education.

I haven't used any of these yet but there's a BP article listing several services Also there is pay near me which IMO is a Good supplement to the online services if you're tenants don't have bank accounts or you want a back up as most don't already include a cash pay service http://www.biggerpockets.com/rei/pay-rent-online-payment-tools/Happy rent collecting

Hence, why I'm trying to have some of my properties work for me-as supplemental income. 

SSI (Supplemental Security Insurance) is a different federal program that provides additional income to seniors in need and the disabled.  

In high school I read a book that listed "assignment of contract" as a way to supplement your income.

I want to start slow doing it part time to supplement my income, money is tight.

We have wanted to own property for several years as a way to supplement and maybe even replace our income in the future, but thought it was just a nice dream to have.

The goal would be to supplement my retirement and make additional income.I'm a full time employed individual with very little cash, great credit and own a two family that has equity.

I'm looking to find a few homes a year to flip for supplemental income and to build capital to purchase some rentals

At least other than the people that don't make any money while holding the place would have all the issues be a bigger issue since all those costs are higher and need to be funded from some other source.I agree with your basic point that cash flow is NOT guaranteed, but if you expect to make $300-400 in cash flow and can't rent it you can always drop your rent at least $300-400 and not have to supplement it.However appreciation sure isn't guaranteed either, and less so the shorter the hold time.