These are 1930 buildings with old plumbing and electrical systems.

I currently work as an embedded software engineer.

There's  plenty of parking however when my relator reached out to concord zoning they said it isn't able to be turned into a duplex " which to me means one address instead of two and I cant have separate water and electricity to the units".

So I’m in a bit of a bind, I have a duplex I’m house hacking we remodeled entire thing, new hvac, electric panels, electric main, updated plumbing, water heaters, furnace, install central air, roof.

I was like no snit but I am not reducing the price as that was clearly visible when you walked the property (which they did)If there is an electrical issue that comes up that is a problem - sure I can fix it or give some $ to get it resolved but for blatant obvious things I do not negotiate as it should have already been part of the offer

The new bathroom will be constructed within the existing structure, and while electrical wiring might be needed, plumbing installation is definite.

I put in a well, brought in electricity, a gravel driveway, a septic tank, and a fence around part of it for my horse.  

That doesn't give them what they need.If it needs a stamp by a licensed Architect or Engineer, that cost would be additional.

If a deal doesn't work if you have 3-4 worst case scenarios in plumbing, electrical, etc... then it wasn't purchased well enough to make it worth the time and effort. 

If the unit has issues such as ingress/egress, bad electrical, is newly developed space without meeting minimum ADU setback requirements, etc then of course the jurisdiction can red tag it and enforce it.