I am aware that Airbnb and VRBO requires city license "proof" in order to list on their website.

Here is one proof point.This past week a friend of mine was putting an offer in on a Midwest apartment portfolio.

I send it with USPS proof of delivery but no required signature verification.

How much time have you spent on preparing a bullet proof lease, with every rule pertaining to your property imaginable?

Get proof of all income.

VAs aren't a silver bullet to solve poor processes.

The underwriter will need to see proof that these gains are consistent with past income and not one-off events. 

Mistakes were made he now has to fix them by making it very clear to his tennats that they are not in control.for me I think this landlord dodged a big huge bullet here..

For example, if a parent co-signs for a child but the child  graduates, gets a job and starts paying the loan that debt can be excluded from the parents DTI as long as there is proof and the payments from the child have been on time. 

There's no magic bullet here.