@Sandra Ho, It sounds like you are talking about late payments on their credit report for things like credit cards, car payments, student loans, etc.

As a generic advice:  I would recommend paying off any credit card debt, or high loans. 

Real estate will not be the get out of jail free card without these things in order.

Also, Credit Card suggestions for best business card for benefits / perks right now?  

Well....should you invest in a city where the people elected a woman with foreclosures, liens, judgements, garnishments, ethical violations from the state ethics board,  misused a city credit card, went three years arrears on her federal taxes all while yelling for other people to pay "  their fair share, " left skeletonized dead bodies hanging over Canal St for months on end covered only by a tarp until the wind blew it off to reveal to our horror her blatant disrespect for human dignity?

I get calls, texts, cards and letters constantly on this rental.

I also due to all the walk-ins put a sign with cards by the front door with my number that way I could kind of verbally take an application when they called. 

You can use a card reader on the coin-op feature to address that, but you are into micro-issues at that point that I wouldn't want to deal with.A proposal: Tenants, installing separately metered water and electric lines that I pay for, then bill you for, will cost me $5,000 (or whatever).

Maybe with automatic payment stuff and you can request changes to your credit card due dates, you can take as much advantage of the float. 

I see 3 days ago a charge for a whopping $390 was charged from BiggerPockets to my card.