Check with local building department, they would be the best answer

Cities have economic development departments, or the like, which publish all sorts of data on demographics, income, housing, schools, population growth, growth, employment,  and a host of other data.

They have a hazards claims department and I was a contractor for them.They would file insurance claims on the properties and we would fix them up and get them ready for resale. 

Legally anything over $600 requires a permit but local building department have total control. 

The best call you can make is to your local building department.

The department of labor statistics says between 2000-2019 housing prices went up 2.38% Nationally.

Find a small local credit union or bank ask for the commercial department.

I will be discussing with the zoning department on Monday.

I'm not sure how the water department's website works where you are.

I would seek legal advice, possibly a formal complaint to the department of real estate and board of realtors and a lesson as to NEVER allow any buyers to have possession of your property prior to close of escrow.