Like all tenant screening tools or services, it gives us all the standard stuff like full credit reports, criminal background checks, eviction history. 

Understanding those unofficial boundaries will help you identify who your most likely tenant base will be and cater to them. 

I'm trying to understand specifically which items add/deduct more than others.

You’re going to deduct the rental mortgage interest against your rental income and your personal mortgage interest (if allowed and more than standard deduction) against your regular income.

If not, don’t even think of this.No matter what, consult a qualified lending attorney to understand your legal options and ensure you have proper loan documents in place to protect your investment.

I am evaluating a real estate deal using BRRRR calculator and need help understanding why my cash-on-cash return (CoC) appears as infinity (∞%), even though I have actual cash invested.

If you think you can achieve higher returns simply investing in low cost markets it means you don't have basic understanding of investment principles. 

I have been trying to be understanding but it has been pushing too much. 

Anyone who has participated in a bad investment understands this.

My point is that when you try to determine "market rent", you need to determine what your approach to pricing is and understand how it will affect vacancy/turnover.