Does anyone know of a reliable site or resource to check zoning laws for Airbnbs or STRs in general?

Think of it like a dating site in that its purpose is to just bring the interested parties together, but if love is to bloom, it will take some work.

Applicant is ok to show me in person his account information on his laptop, but doesn’t want to put his user name and passwords to those sites into RentRedi application.

It provides links to each county office's sites for when you're doing research. 

HUD publishes the Median Fair Market Rent on their web site for the entire country.

I would make a site visit to where they live now and see how they treat the current property.

It is usually a tenant moving to a new area, because of a new job and they just want to be done with their trailer.I have had the disgruntled situation come up when I stopped using the on-site maintenance man and made him pay full lot rent like every one else.  

Look at Listed properties, open houses, for sale by owner (FSBO), wholesalers deals, any on site auctions you can find, and look at as many deals other investors own that they are willing to show you. 

I wouldn't be investing in any new city without spending a lot of time on that site first.

Starting smaller is fine, but the unit has to be spa like or you will likely fall victim to pricing wars or get lost in the booking sites algorithms.