I would hate to feel like I am taking advantage of his kindness and would like to demonstrate a proven track record of investment success before accepting an offer like that from him (even though this current offer is admittedly somewhat similar).

If that checks out they must have a verified history in their jobs and demonstrate a sense of stability.

Are there examples or case studies that demonstrate how property tax hikes have influenced the housing market? 

My recommendation is to discuss this people who have a demonstrated interest in trying out different investment vehicles besides 401Ks, IRAs, and pensions.

What you will find is in a few years when you have demonstrated success lots of these people will start asking you about how you are doing it.

With every question he asked them they were able to demonstrate that I had informed them well (plus I had it in writing from them). 

How does one demonstrate non-payment rents to SBA to get these loans?

We have demonstrated our ability to be reliable and to close deals.

Congratulations and thanks for sharing.You’ve certainly demonstrated perststence.Well done!!!

I've found that sharing this form with customers demonstrates accuracy, and RE investors who are rehabbing can use it for comparing contractors/subs.