How to convert an owner into a tenant

[Luther A.]

According to this video: 

https://www.youtube.com/watch?v=yKg5ca8Em30

This guy converted a pre-foreclosure owner into a paying tenant. How would the numbers work on this? From my experience the mortgage is usually higher than rent. If you subtract Repairs, vacancies, property management there is not going to be much left. May even go into negative cash flow. Would you guys know how to make "subject to" deals into rentals. I just dont see how this would work.