I'd want to seal the deal & write it up as a seller financed mortgage for $1200/month.

does the water heater need regular maintanence, what is unfinished that the home owner needs to take care of (grout/concrete sealing, fence stain/protection, etc.)  

Someone moves the shower head around and it ‘breaks’ the old seal that’s on that threaded connection, and it starts dripping down the wall.

Two coats will seal it.  

I have spent hours...days, trying to seal any possible entrance into the house to no avail. 

(to seal it).

The problem is not cats are under the houuse.The problem is the house has openings in the skirting, where the cats come in and out.So will oposums, who the cats tolerate in there as walk through guests who eat the cockroaches.Use chicken wire or wood to seal up all but their main enntrance.Call them out --kity kity kity -- while shaking a bag of purina cat chow -- with a loud shake sound.

House is empty, but husband sees all the bedroom doors removed and nailed crosswise  on the walls leading into the Kitchen to seal it off from the rest of the house. 

They have come out with a laminate countertop that looks like granite, as a less expensive option.If you do go with granite, make sure you seal it as frequently as you are supposed to.

His "final exam" was opening a pipe with an acetylene torch and then sealing it back up... while it was pressurized with natural gas!