Have you pulled title on the property? 

He obviously signed a false statement.The buyer has a claim against the title company to pay the lien - and the title company has a claim against the seller.  

I have never pulled a permit for a water heater swap, know no one that has ever pulled a permit for a water heater swap, ever seen or heard about one getting red tagged for no permit, and have never had a plumber recommend getting a permit.

You posted a video of yourself and presumably your business partner walking around an apartment building with him wearing a name tag as units were being furnished and clips of yourself being interviewed on the buildings common area roof deck. 

If you're lucky enough to get a free and clear property where the seller is willing to finance, this reduces much of the risk associated with seller-finance.I would make sure the title is then moved over to your name, especially since there is not a risk of a due-on-sale clause being triggered.

Thanks for tagging me @Denver McClure.

The previous owner claims they never had the titles to these trailers, so that is not option. 

I confirmed with title and sure enough, everything was there!

The title is in the name of her sister (my aunt) and my mother’s husband (not my biological father).

Rewey: There is a video (free on YouTube) by Attorney Jeff Watson titled "How To Do a Subject To And Do It Right" that I highly recommend.