Tony wrote:

This is a question about what to do in handling a problem with a
contractor. I'm in a quandary. Please excuse the length of this post.
I've tried to boil it down to essentials.

Having heard the prices, I would have elected to do the job myself.
You could rent a trencher for a couple of days and do most of the work on
that end in probably a few hours.
Just lay out a gridwork of ropes as to where you want the trenches dug and
go for it.
The biggest headache of the job is connecting the pipes and the heads to the
pipe.
If you're not comfortable with the electrical wiring, hire an electrician
for a couple of hours.

You wouldn't necessarily need to cover the entire area as water will wind up
filling in what little space there is left naturally.

To make sure you cover what you want, start with one head installed closest
to the source.
Watch the pattern it makes. Then the next one will be set less than that
distance so they overlap.

On a plot 1//3 acre in size, you'd only need heads on the perimeter anyway.
Probably no more than four. One on each corner.
Perhaps one in the middle of the longer sides if necessary.

As for how to handle the payment problem, give the guy 1/4th of what he is
due and tell him to finish the job the way he was told to. If he balks at
that idea, tell him he'll get 2//3 of the agreed upon price or nothing. Plus
some not so good public relations. He'll do the job right. And may even drop
the price.

I do not give legal advice as I am not an [your] attorney.