We actually meet the guy sitting on the front steps and see how persuasive he is.

|It is all the persuasion any tenant should require to encourage them to pay rent.

Let them know that you are there to gather information and to help them find answers and solutions.I would recommend books on persuasion and understanding human nature.

sending eviction-type letters can be persuasive enough to scare the tenant into paying the full amount, but try a friendly conversation first.

Or maybe you are just more persuasive!  

Be honest (and persuasive) with your intentions: you want to win in this deal, but you also want him to win. 

Introduction to Negotiation: A Strategic Playbook for Becoming a Principled and Persuasive Negotiator from Yale University. https://www.coursera.org/learn/negotiationI recently started taking this class and have found it very interesting so far.

(Also, not sure if my wife is on board living in an old building while we fix it up..haha that might take a lot more persuasion)

I'm also a fan of "Influence: The Psychology of Persuasion."

Entertaining and informative reads with great insights and highly persuasive arguments.