It wasn’t until I spoke with the tenants that he revealed to me he had deposit money with the seller.

He was very gracious with his time and answered all of my questions and he even revealed that he was previously a board member of the local apartment association (of Northwestern PA).

An obituary might reveal some names.

The inspection revealed some electrical and waterproofing of a crawl space. 

Can you do accounting, graphic design, perform acupuncture, maintenance?

Do you have access to the funds to throw into a money pit should one reveal itself.

The replacement of the windows revealed more hidden rot which was a good thing it was discovered but led to some undoing of work I had already paid for at the beginning of the project on the exterior.

The kitchen was remodeled, new appliances, granite, knocked out part of LR wall for open-concept kitchen/LR, tore up carpeting throughout to reveal hardwood floors, installed LVP in 1) kitchen and 2) den-turned 4th BR, upgraded toilets, painted entire house including pine planks and paneling, and crown molding,  installed sliders to backyard.

If they are being shady and not willing to reveal all the information you need for the deal, you may want to walk away.  

You can do a background with a TIN but it may not reveal much.It is possible to be here on a TIN and not be legal, plenty of people with a valid TIN may not be lawful residents if for example they came on a visa and that visa was not renewed.