I know this not acceptable so I am thinking I need to remove the debris, spray for mold, paint with mold resultant paint on the joint beams to be safe, lay insulation plastic over the dirt.

I would consider it B-.We had some reputable boots on the ground and without that, not sure if we could have done so. 

A couple of hours later my thermostat started smoking and burnt up melting the plastic and leaving a mark on the wall.

Their reputation means too much to them.

You dont have a brand yet, that comes with a reputation.

Locally is not an option as I'm in Toronto :) The company is very famous and reputable so I don't think they're being shady.

Bought a foreclosure with a wall that appears to be made up of 2x3 walls sandwiched together with some weird hard plastic membrane between them.

Know what your doing and use a reputable attorney

If you do recommend, where do you find reputable people to work with? 

@Scott DeMichele I’m glad to hear that Bigger Pockets has a great reputation!