Mold requires two things: moisture and a food source (dust is sufficient).I suspect this is on an exterior wall in a cold climate.

Has there been a change in political climate and attitude towards business and growth? 

Climate controlled storage is in short supply in my market area of Sioux Falls, SD.

I will mostly echo what @Thomas S. has said:service oil furnaces once a year, oil burns dirtier than gasService natural gas furnaces every 2-3 yearsAC I would get serviced yearly in warm climates, every couple years in seasonal climatesAs a landlord I would always make sure you are coordinating these services yourself.  

They all will probably reduce your bottom line and aren't things that looks fun in a picture though.Everyone blames cars for greenhouse gases and climate change, but in fact buildings are a much larger contributor.

Also sometimes you will need to pick up the bill to save yourself more loss.Example: Property A is located in a cold climate like Cleveland, Ohio.

There are significant "why nots" though - specifically relating to the "climate change", "zero emissions", "no plastics", etc initiatives that are out there which would be more detrimental to these projects.Account Closed Might not be what you're looking for, but I wanted to give my opinion on something I know.

I don't live/invest in a climate where I have to worry about things like that, hence my ignorance.

A vacation rental takes more money and effort to produce the same results and is more likely to be impacted by a change in the political climate or the next internet invention.

I’m not sure if this is the reason for your feedback on the windows as I don’t know the climate of your market.