Normally written contracts are strictly construed, but if they are vague or ambiguous then verbal supplements are involved and you have no knowledge of what those are.I do have some words for the advice of @John Thedford ...

When it comes to details around financing, regulation and taxation, much of the information is U.S.A. specific and those of us from elsewhere need to find local information sources to supplement.  

Some investors do both (or use one to supplement the other). 

And that can supplement your r/e experience and since you will want referrals once you go full-bore into r/e you will have seen both sides of the equation (referrals are leads generation).  

Looking to make some supplemental income.

My name is Ivan Ivanov and I live and invest in Pittsburgh. 5 years ago I purchased my first rental hoping that the income from it will supplement my retirement.

My goal is to grow my income and supplement my life with wealth other than my W2 job. 

@Lee S.I am now a licensed salesperson and I would like to use it to supplement my income while I work on closing more wholesale/flip deals.  

Supplemental tax bill? 

Don't forget umbrella insurance policy as a supplement to protecting significant assets or just protecting yourself from liability cost.