@Elliot B.I doubt a energy meter based on airflow, heat - etc - of any variety - would hold up if challenged in a court of law - 

Revisiting this post, I would strongly recommend any service-based business where you can buy in at a low EBITDA multiple.

Quote from @Dan Deppen: One that I've seen a few times is people thinking they can sell a note based on the sum of all the remaining payments instead of the principal balance.  

The Top 5 in my search so far based on minimum requirements. 

And finally, while there are likely some pro accounts that will only give you discounts if you are licensed, most will let anyone sign up, and are often based on volume spent at that store anyways.

Land doesn’t depreciate, and while buildings require maintenance, they usually gain value as markets grow, demand increases, and inflation takes its toll.Real estate investors benefit from a significant tax write-off based on the concept that properties lose value over time, even as their market value skyrockets.

Forming little groups in the background to down vote certain individuals comments based on skin color, or religion, or perceived political leanings seems like something we could all do without on this forum.

Value based on NOI and cap rates.  

Their cap rate is based (among other things) on the current property taxes that they pay.

When managing the "security" this mortgage is a part of they probably have a strategy for how to manage that is based on keeping a stable known risk for the security.