I don’t know what’s going on of course, but I can offer the possibility that the seller tried to negotiate the bill down and the contractor realized he was being squeezed so he took action.  

I recommend getting an insurance indication from an insurance broker, a debt term sheet from a mortgage broker, and property tax guidance from either the county tax assessor or a real estate tax consultant. 

Insurance cost is a huge problem here for all Associations.   

Quote from @Brooke Morton: Does anyone have recommendations for condo/HOA insurance?

Hello, does anyone have a small HVAC contractor that they can recommend in the Indianapolis area? 

Your knowledge of contractors in the area3.

The cashflow should cove ALL of the expenses for the primary (mortgage, taxes, insurance, utilities, etc) AND put money in their pocket.

Some people will say, "Take out a quality Insurance Policy and you will be protected."

Also, the insurance was a lot less on a brand new home compared to an older one. 

You may have to search a bit for the right contractor or engineer - sometimes I see one solution dominating in an area - "that is how we always do it"