The appraiser also seemed to exclusively use Zillow to find properties and 2 of the subject properties had their leases end this year. 

I have a lot of thoughts on this subject and will try my best to keep this concise.

Let's say I have 500k down payment and borrow 500k, and the monthly mortgage payment is 5800, and out of that, 4800 is mortgage interest, and I pay 2500 annually for insurance and 10000 for property tax, could anyone please let me know how much UBIT I would be subject to?

Hey @David Cherkowsky - going off of what Jaron already mentioned, there's no real "tool" to track appreciation because its very subjective based off of whats been selling in your area. 

Computers can calculate square footage, number of beds/baths, and other objective criteria, but they can't measure the subjective things like curb appeal, flow of the floorplan, view out the living room window, or the grating irritation of four barking dogs in the neighbor's back yard.Learn to study the market and how to evaluate properties on your own.

This shows your complete lack of understanding about the subject.

I doubt the contractor wants to foreclose subject to your first loan..

You also subject yourself to possible discharge of loan if the borrower files a bankruptcy.

Wholesaling is earned income which is subject to taxes.

He is an advocate of subject-to financing to purchase properties.