What the consensus when you run into nasty wiring? Told h/o today that the existing cicuit connected to my work,shouldn't work
(it's a gnd/nuet. fubar).Twist his arm to get it right?;or something legal to shield me?

How is the existing circuit connected to your work if you didn't do it?

Maybe more information would help.

I made a new ceiling light in l/r,box, circuit etc.,powered out of jb marked l/r 3-way.Check power to switch,OK:turn it on,no light.Tic tracer showed hot at fixture; in course of checking noodle back,found 1 in jb nutted to bundle of bare grounds;take it off,
nut it to 'my' white,still nothing;put both whites on the grounds;it works.At THIS point I explained the 'fubar' to the h/o;I'll have to take the boxes apart in the attic space,etc.,i.e more money, and his reply was to "leave it , it works." Some now deceased family member had wired the attic.

Yukk. If it were me I wouldn't involve myself in the existing mess.

I might go as far as using existing wiring and boxes in order to avoid breaking walls. But if there are other cables in, say, a switch box, that don't make sense I wouldn't do that either.

If something gets goofed up in there you'll likely never find it.

Iwire will probably be here any minute to point out legal stuff.

Derater,

When I was in business, if I found a small "fubar" I would tell the homeowner and then I might just fix it myself and tell them "No Charge". It was good for the business. However if there was something real bad, I would tell the homeowner and make them aware of the problem, ask them if the wanted me to fix it or give them a quote to fix it. I would fix it unless they told me too. ( Or get a change order.) If they didn't want me to fix it and just wanted a bill for what I did, then on my bill I would write down what I saw wrong. For example: we added 3 receptacles for $55.00 a piece and while on the job we saw that the sub panel was in violation of the NEC. If you would like a quote from our company, please let us know and we will submit a price to repair the problem.
I figure that if the person saw my bill and paid me, then they would have read my note about the violation in their house.