I've seen a few people who were trying to get a leg up as a beginning investor have plan schedules that moved faster than government and not realized some of the more hidden costs of subdividing.

They are the gems!

The hidden cost of being passive and having a PM is higher repair and maintenance costs and your never being there to see it. 

You do not mention, but if I were to guess this is an older home, with YEARS of dust and who knows what waiting to shake loose...if hidden dust was a major concern, they should probably be looking at much newer properties.

Finding hidden problems during rehab.

My electrician told me there's a new national standards that says if you replace receptacles, the new ones need to be the tamper resistant ones with the hidden slot covers inside.

Tax sale is very risky and full of hidden costs and risks. 

New tenant request from actual people (their personal information is slightly hidden).

(my best homework at the time, I thought that gave me a great margin and enough room to cope with any potential hidden issues).

Also be sure to ask if there are hidden fees for things such as overages, appliance disposal fees, or hazardous waste fees.