This confuses them when they jump to commercial real estate, as commercial real estate operating expenses only use the ITI, and not the P (Principle mortgage reduction). 

I understand that having a piece of real estate, where the numbers work, is key to having a good deal and not to short sight other components such as property management, contractors, etc...

Purchase price: $300,000 Sale price: $400,000 This investment doesn't fit any of the categories available, but it uses multiple principles discussed regularly in BP.Properties: Two side-by-side, shared-wall commercial/retail units within a historical street retail district.

Some general principles that might be handy: if the debt isn't getting in your way, consider whether you would make more with the investment than you lose with the liability.

Other than that, both of them hold the same investing/landlord principles. 

Say the 3 points ($2,314.20) are rolled in, bringing the initial principle to $79,454.20.

I am thinking of things (situations, principles, actions) that have ACTUALLY moved the needle for you now that you look back with hind sight. 

So we ended up with some of our principle back and 2 promissory notes.

For some, time is money, and if that's true, the Time Value of Money principle quantifies things, and personally I think it's one of the best ways to quantify your personal time, especially for a quant-nerd like myself. 

We used to have a duplex that the insurance alone was more than your entire cost estimate (it was in a high risk area on the beach).The 50% rule is the standard starting place for estimating expenses not including mortgage costs (principle and interest).