Did you apply closed/open cell spray foam - or strap and use packed cellulose/hemp/fibre - the outer walls and underside of the roof deck (requiring an over roof) or did you maintain ventilation under the roof-deck and insulate over your ceiling?

The other is to not add any insul to the other under side and leave it be. 

If there is a dirt floor in the basement, be aware that the excess moisture can rot out the floor from the underside and can be more prone to pest infestation from burrowing. 

Several other sections have visible rust on the underside as well.Recommend having the pipes checked by a plumber, and replaced as needed.

As for what the agent should have known: You said it yourself that everything looked good when you went in and that the damage was spotted on the underside during inspection. 

But after a bit I spotted something.See the water on the underside of the pipe?

I guess: 6 hours to paint (including dry time and touch up), an hour to pour, over the first few hours I have to keep brushing the edges and catching droplets on the underside, and then 2 days to fully cure. 

Good, not meaning to be insulting, but this stuff kills people.While it is not running, take a close look at the vent pipe, especially the underside or side closer the basement wall.  

I know you're not going into a house that you are seeing for the first time and having the owner follow you around for 1 to 2 hours while you measure each room, walk the roof, crawl through the crawlspace, inspect the underside of the roof in the attic, checking each squeaky door, and so on. 

Personally I'd want to see the seat up in a picture so I could get a general idea of how dirty the bowel could be and ensure there are no mold stains on the underside of the seat.