It does not appear that you are asking the question.... It appears that you are stating that your builder is incompetent.

Footings here are normally not vibrated. Without pictures no one can tell. Are reinforced bars exposed?

Ask the architect or the builder to explain to you the quality and details of the construction. They are there and can know the specifics.

The building codes here state that the rebar from the footer must be 12"
or less from the top of the wall, but with rebar only extending 18"
above the footer...

That's 12" or less from the top.

I've never heard of vibrating a footer and have never done it. In fact, I don't know how that would work as the vibrating head is several feet long.

Without pics or the builder's approved plans, or even the relevant Codes it's hard to comment further.

If you're serious about this purchase have a structural engineer look at it. You mention several things that sound sketchy.

Thank you for your comments and advice. In terms of local
building codes, the operative ones here are IRC R403.1.1 for foundations and
ACI 318 for rebar. #4 rebar is the standard, overlap for splicing is 16”
minimum, footers require two rebar beams, foundation walls require that column rebar
be within 12” of the top of the wall, and rebar spacing must be 48” o.c. for
2-4’ walls and 18” for 4-6’ walls.

I contacted the builder about my concerns by email the same
night that I made my original post. He responded the next morning that he was unfamiliar
with the local building code, and had relied on the engineering plans plus the
concrete sub to get it right. The next day the 18” high column rebar had longer
rebar spliced to it with at least 16” overlap to meet the height requirements
of the walls. However, I noted that the
height of much of the planned foundation wall had just been raised to 5’ from 4’
as marked on the footer. I emailed the builder that night that by code, the
rebar spacing would have to be tightened to 18” o.c. from 48” o.c. The next day
most of the 5’ wall was reduced to 4’, so that the column rebar spacing could
stay at 48”. However, some remained at 5'. Since the footer has been poured, it would be
very expensive to emplace column rebar at 18* o.c. for the section of 5’ wall.

I met with the builder on site today. He agreed that the
workmanship of the concrete contractor on the footer was very sloppy. I pointed
out the honeycomb zones through the body of the footer where pours did not meld,
and potential risk of rusting the rebar beams in it.
He said that he would take pictures and consult the engineer. My
pictures are attached here. Your comments are welcome.

So what went wrong? The builder does not appear to be
thorough when it comes to reading building codes and community codes (I caught
a huge problem with the house footprint size as a % of lot size of his design before
he submitted it to the HOA for approval).
As a result, he relied on the engineering plan and the concrete sub for the
foundation work, and did not scrutinize it. In fact he said that an approved
engineering plan trumped the local code, even though the code states that it is
part of the approved plan. I am not sure
who is right since I am a neophyte. It is very hard to find good subs due to a
building boom in the area, and one takes what one can get I am told, or one
waits. While the soil drains well and probably has a psi of 3000-4000 (my
guess), it has a lot of boulders in it. As a result, a relatively inexperienced equipment
operator dug the foundation much deeper than planned, causing the foundation
walls to be much higher than in the original engineered plans. The irregular
surface made setting the forms more difficult. The concrete contractor may have
worked from the original plan, but it should have been obvious that there was a
big problem if the top of the foundation was to be far below the grade. The
builder said that the concrete contractor claimed to always splice its column
rebar like that. Dry concrete
probably contributed to the high degree of honeycomb and air pockets throughout
the footer. In any event, people interacting, reviewing plans, and thinking would have helped immensely.

My wife really likes this lot, and the
builder says his crew takes over from here for most of the work. I am not
locked in at this point (builder’s choice, he prefers to spec, but has been
working with me, and is honest and communicative), so I simply want to make wise decisions.

Just working the concrete a bit when pouring it into the forms would likely have avoided that mess.

Though one can't see it, I wonder how careful the crew that poured that was with the ground prep. IOW, the soil on which the footings are poured must be undisturbed--which means not even walking on it prior to the pour.

Completely agree on working the concrete...a little more thought and effort during the setup and pour would have resulted in a much better result.