Most charge off of gross plus other hidden fees.

But from experience, there is usually a lot more work than expected, hidden problems, and they turn out to cost a lot more than you budgeted.

I focus on "actual" cost, instead of "total" cost, and numbers with "$$$" in front instead of numbers with "%%%" behind, and found (Created) more deals out of thin air (OK...maybe a little less thin), than the obvious ones that everyone can see...and then end up competing with eachother for.I learnt that almost all solutions to every problem (not just in REI), are hidden right in the problem...in plain sight. 

3 different types of plumbing = hidden joints and connections behind the walls that weren't put together properly and will burst when you least expect it.

My parents assisted me with the remodel and after 9 months of hard work we transformed this gem of a property.

Obviously the great PM's reduce that risk, but there is always some amount of risk for it.Also, hidden clauses that require the landlord to use the PM for selling the property. 

This made me giggle - as a real estate agent/broker we should all be used to spam and junk mail and buyers/sellers that aren't real...it's part of the gig in my opinion and it's always fun to find the true gems out there.

My 1st exit Strategy is to wholesale to an investor that has more capital to invest, but I cannot shake the eeling that I would be letting a gem go.

@Darshil Parikh So what numbers are you using for your hidden costs:vacancy, repairs, capex.

Hidden gems in the answers here, for sure!