Usually they have several code violations which are significant safety issues- the biggest usually being a lack of fire protection between units. 

Water is the single biggest expense in my N.

My take is the City of Portland, the biggest landlord in Multnomah County, is the root cause of rent spiking drama.

That would be my personal suggestion, but however you structure it isn't the biggest thing.

I know that in the beginners guide it says that your biggest marketing tool is "yourself" and I believe this 100%.

Labor is my biggest expense.

The biggest factor will be your risk tolerance.

This seems to be my biggest obstacles for the last 4-5 flips that I did.

What have been the biggest mistakes you've made? 

Fix and hold really isn't what we are looking to do at this point, but it made the most sense for this property.At this stage, our biggest issue is trying to figure out financing that will allow us to queue up multiple projects at a time (and not miss out on good deals because our capital is tied up).