@Bernard Reisz Another important question to keep in mind is what methodology is being utilized for the report as there are six commonly used methodologies that are recognized by the IRS.

If you have hired a specialist to perform a cost segregation study of your real estate property, they will likely use one of the six most common methodologies recognized by the IRS.

@Phil Shelton  The IRS' recommended methodology is an engineering-based study.

I've recently been introduced to the Profit First for Real Estate Investing methodology and I'm excited to implement it! 

Now via methodologies such as BRRRR (or any value add associated with a refinance that extracts value), the $100k property can be owned with $0 investment producing infinite return.  

It is implied that the methodology is fair.I always charge my tenant for water to encourage conservation and reporting of leaks. 

This article is written from a Canadian perspective but still desceibes the methodology well, recommend you check it out.

The IRS' preferred methodology is engineering-based which costs more.

Zillow even publishes their accuracy rates on a county by county basis, and they are transparent enough about their methodology that anyone who bothers to look at how they come up with an estimate would realize that it's worthless.  

The approach I use now is actually very different from the one that Jack lays out in his course (I don't use a lot of his exact methodology anymore), but he did play a major role in making me aware of the niche in the first place, and it helped me to identify what does and doesn't work well with my own personal style.Anyway - all this to say, Jack's approach is legit.