Rust/ corrosion was observed at the panel box or breakers.

Plumber went today and explained pipes are blocked, and some corroded (expected with the age of the property), but unable to say where the block/corrosion is to quote properly until they "start to dig". 

All cities have their own problems...Las Vegas desert water cause a lot of pipes corrosion and water leaking issues.  

Maybe would try to investigate with through the fill pipe with a borescope for some corrosion holes and cleanliness of the bottom to understand potential spill potential ($25 on amazon).Good luck!

If that isn't fixed correctly, the corrosion will get worse over time until you get to the point that the mesh no longer serves its purpose and begins to detach from the house.

Bleach is extremely corrosive to humans and has cumulative affect when exposed.

Also reduces corrosion and buildup on the pipes.Did the occupied side of the duplex have a softener installed? 

Check the ARV's for corrosion etc., as it's imperative that the air/gases generated are passively removed.

Are their cast iron pipes, and is their corrosion, when was the main sewer line replaced between the street and the home?

I recommend that a corrosion analysis (I like to used the Baylis curve) should be done when you are doing due diligence for a park that has galvanized pipe.