Slick camera work and computer image manipulation suggest producers of Hancock, the action adventure released for the Fourth of July weekend, exceeded their rental agreement with Bonanza Concrete Inc., Van Nuys, Calif. In reality, production crews painted a wreck of a mixer to mimic a perfectly capable vehicle — now back in the Bonanza fleet — that appears briefly in one of the film's destruction sequences. A member of the shrinking pool of independent concrete producers serving Los Angeles County, Bonanza has a long track record of loaning and renting vehicles for film and television appearances.