For new rentals, lenders compute the net rental income using:  net rental income = (rent * 75%) - PITI.

You need a contract to buy at the loan amount, the seller needs to get a loan payoff so that you can compute the interest to the day of settlement to be used as the sale price.

Debt/Income = your DTI.Step 2: Compute the net rental income. 

And what if you have an older tenant who isn't computer savvy?  

If I have to pay 3K out of pocket to get the loan it is the same thing as receiving 97K without me having to pay, the allocation is, as required for the APR computations, that the borrower received 97K as Dion explained.

I also work for an industrial computer provider and have for the last 18 years.

And, since most throw business cards out, they will have a copy of yours if they at least keep their emails.Scan or photograph the cards of anyone you even remotely think you might need and file them in your computer by name.

I avoid all warranties cell phone, TV, computer etc.

If the target population is one that uses computers all the time then it may be the timing of the application.

And I've had almost brand new furnaces require significant repairs.You can, and should, use the 50% rule in combination with your other assumptions (market rents in your area, financing) to compute what you can afford to pay.