I bought the lot 10+ years ago to prevent a slash-and-burn developer from getting it and putting a home that wasn't right for the historic neighborhood (it's not designated, modern homes look extremely out of place here).  

This has prevented me from getting into residential and drawn me more towards commercial, maybe that is a false assumption.

Ultimately it may be in your best interest to take care of it and may be required by law depending on the state.Rats don't squeeze in under a door, not a normal door at least, so I would first make sure that all outside cracks, crevices and holes are filled up, especially in a crawl space to prevent anymore from getting in.Then, again it really depends on the state laws, but after my due diligence is done sealing up the up the outside and inside of any places a rat could get in I would think about telling the tenant that they can buy rat traps or whatever they want to use to get rid of what's is inside and I will reimburse them the cost with a recipe, I would only do this if I felt comfortable with local laws otherwise I would just hire a pest control person to take care of it.

The home owner may have filed the BK for legitimate reasons, but as far as including the home that is currently going through a foreclosure in a trustee state is concerned, the CH 7 BK will not prevent the sale.

For example A GRAPE DRINK stain on a carpet will be damage when found immediately as opposed to normal wear and tear 3 years down the road when they move out. 

(J) "Disabled licensee" means a person licensed pursuant to this chapter who is under a severe disability which is of such a nature as to prevent the person from being able to attend any instruction lasting at least three hours in duration.

To prevent it from being a true second full apartment and maybe violate zoning codes or maximum occupancy it would have no actual cooking facility of a stove.

It requires about $7.7k in concrete and dirt removal and replacement to prevent water from entering the house (as well as fixing the windows and drain pipes).

Stains/scratches on the flooring with a rule next to them so the size is known, pictures of the place being dirty with a statement from the cleaners you hired, etc.  

I walked into a 55k triplex with drop ceilings stained and falling down, rats fighting to get off sticky traps, no HVAC or separate utilities, and the back foundation dropped so much the floor buckled.