The owner is friend of mine, really good dude.

Have used state programs to upgrade all windows, insulate, instal 3 mini-splits in main home, 1 in ADU in main house; turned garage building with 2 ADUs from oil heat to mini-splits.

In most cases, it's probably not worth the effort.Wall insulation:Acoustic insulation: Fill wall cavities with fiberglass or mineral wool insulation to absorb sound.

Would you want a honda mechanic to change the oil on your Porsche?

But auto shops, particularly "backyard" shops are generally not the most careful with their used oils, brake parts cleaners, and other nasty chemicals that could be a real issue for your tenants and ultimately, you, the owner.3.

If not cleaned well, dried, and oiled regularly, cast iron can rust.

thats basic list one can add.Value add /  New construction / land entitlements/ Timber / Minerals/ Lendingetc etc.. far more ways to actually make money than just buy and wait for rental income to payoff debtl 

We have converted oil boilers  to gas boilers to reduce costs. 

.: Oil is used in about 4% of homes.

He's not a scammer stealing money from people, but he's definitely selling snake oil.