You are correct... Section 24007 (b)(2) of the Vehicle Code states it was
the responsibility of the seller of your 2005 Ford Mustang to provide a
valid smog certificate at the time of delivery of the vehicle. There is no
provision in the law to sell a vehicle "as is." Therefore the seller is
always responsible for the smog certificate even if they mention the car is
sold "as-is" because the law doesn't recognize the "as-is" policy as it
applies to the smog check.
You now have the option of paying for any smog repairs necessary to get your
Ford Mustang to pass the smog check but may need to take the seller to Small
Claims Court to recover your costs. Although the law clearly supports the
buyer, collecting on a small claims judgment can be difficult, so the
amicable solution is usually best.
We have to recommend contacting the seller persistently advising that you've
spoken with multiple agencies and if need be you are prepared to take them
to court.