A lot of different factors! 

The Section 121 Exclusion helps you avoid capital gains taxes.The IRS classification of income as a "Flip" for Real Estate Dealers is based on a few key factors including "frequency" and "intent". 

What methods or factors have you been looking into when choosing properties for your portfolio?

An $800,000 Single Family home with an 8% interest rate earning $300 a night with an occupancy rate of 60% isn't even close to profitable once you factor in every other expense, and yet there are Geodomes that, if you want to be generous with the construction cost, might cost $100,000 each that are earning $200 - $250 in the right area, with the right management.

Once we build the relationship everything is just flowing.It'll work, but in California it may be harder because you got to factor above average appreciation so your spread between with lower downpayments/higher DTI and A to B, then again A to D may be really hard. 

Most of the " we will help you stay in your home companies" got put out of bizz during the GFC since so many were just fraudsters .If someone is in foreclosure their credit is ruined at that point going to foreclosure sale does not matter on their credit enough to make that a  motivating factor although folks BS about that too.

Obviously the answer I'm sure depends on a number of factors (affordability, reliability, etc.) 

Price and timing depend on a lot of factors.

So be sure to factor all that in.

For a more accurate financial projection, factor in these additional expenses separately.