If so, I'm not sure what the grounds would be unless part of your written agreement includeds a right to recover the property if the buyer failed to make the payments.However, even if you have a right to rescind, I suspect the title you recover will be encumbered with any liens or judgments your buyer and his successor caused to be placed on the property, including any judgments other people he defrauded obtained, judgments the state or Federal government obtained in prosecuting him and any liens recorded for failing to pay taxes on the proceeds of the fraud.I think you need a very good attorney experienced in this type of situation to advise you of your options. 

These old houses sometimes have sewer issues, and this place looks like Roots City International.To me the house looks "Cared About", I see some proper looking wood trim under the porch, the porch columns were not replaced with 4x4's, all windows match, etc...Plus this house might have an interesting set of interior upgrades such as built in shelves, etc...I say that because the front door looks like it has 2 side lights (a big upgrade in the olden days).And I suspect the stairway may have some elegance to it, such a a landing where that small window is.With all of the close in trees, the gutters may be full of leaves and you may find rotting wood at the edges of the eaves, and many of these old homes a have boards under the shingles vs plywood, so you only talking about replacing a board vs a big rectangle.Good Luck! 

I suspect the family didn't fight for it because they didn't want to take on the liens? 

Phoenix has gotten really bad with all the shootings and homelessness and I suspect it's going to get worse before it gets better.

I suspect I was almost cut out of this deal by a more experienced investor (my guess is they were waiting for my contract to expire so they could swoop in).

If mold is suspected in the ducts, you could consider having the ducts professionally cleaned before replacing them to see if that helps.I hope this gives you a starting point for further action, and I truly hope you get this resolved soon.

A smart seller might ask for some kind of limit to the Subject-To financing but I suspect that many don't because they are facing foreclosure and therefore aren't buying another house anytime soon.

Sub-to's still have a place IMO, but the Guru's may soon have to start re-thinking their sales pitch to the newbies...and I suspect those who continue to sell these on wraps may be want start picking out a good attorney as I imagine we'll soon see class actions and likely some more state and/or federal legislation. 

I also want to put a strong emphasis on what John said.In 2020 there was a "fund syndication" that was investigated by SEC as it promotes real estate with fraudulent mechanisms and is suspected as a ponzi scheme. 

Are you suspecting volume of sales to crash or prices to crash?