State officials have announced a crackdown on used car dealers who sell automobiles that do not meet smog control device requirements throughout California. Buyers of such cars get a shock later when they have to pay substantial sums to fulfill these requirements in order to license the car. A recent undercover shopping investigation in Sacramento and Placer counties found smog equipment violations in about one-third of the vehicles offered for sale, said John Grew, chief of the Bureau of Automotive Repairs of the Department of Consumer Affairs. Grew advised prospective used car buyers to have vehicles checked at a licensed smog control inspection station before they sign the purchase agreements. He also said used car dealers who offer vehicles with improper smog control equipment can be fined up to $5,000 a car.