They did some prep work (picking up some stuff in the attic and also hanging duct work which is probably unnecessary) and then wanted payment for materials and what they just did.

That is completely unnecessary and a recipe for failure.I'm also sure that you have your own bag of mistakes that made you the seasoned landlord that you are today.I certainly made a few mistakes, but only a few.

I've had two tenants use these extinguishers to put out kitchen fires with their extinguishers, thereby preventing major damage.

This may sound too good to be true, but she is motivated to move, and the current mortgage procedures and qualifications are preventing her from selling to the general public.

If they will not waive their rights, you can file for bankruptcy protection right after the close and this could prevent the lender from filing a judgment against you and discharge the deficiency forever.

Just to clarify, a purchase and sale agreement would prevent another investor from stealing the deal from me?

Dima, slightly off topic, but one of the things you want to do to help prevent lawsuits is to keep the property in tip top repair.Respond immediately to repair requests and always walk through the house with your eyes looking for anything that could be slightly dangerous.

Anyway, the meters that I use are "tamper proof" which is really "tamper evident" since they don't really prevent you from tampering, they just make it obvious that you did.There is a wire, with a lead "seal" that cannot be duplicated once broken. 

The local nature of real estate investment prevents any large firm from "dominating" the industry so to speak.

This of course is under the assumption that the realtor gave you correct comps and that the prices in your area aren't still falling, in which event may prevent even an owner occupant from bidding.