I walked in one (owner lived in the same building), were the tenant had a tarp in the kitchen due to a months old roof leak and they were using the gas stove to heat the unit. 

But that is the way to test; you also will want to close shut off valves as you go along to isolate sections once you know their status (a section leaks badly, stop testing it).And you will use much lower pressures if you are checking gas lines for leaks. 

Cheap natural gas will decimate coal use over some period.Have you noticed how fast LED bulbs have replaced small incandecent bulbs?  

Yes, those are some valid points.  

Thanks fellas those are things I thought of just was seeking the validation or if someone had a super secret method..  

I would want to know how valid the claim is, how well documented the damages are, etc.

But my tenants pay for all my needs, my vacation home, my utilities, my food, my gas, and are paying for my rentals.

The current heating system is natural gas with old cast iron hydronic radiators.  

Going on site and Validating probable investment candidate property.

You live in gas city?