This study develops an analytical framework to examine the interplay between deepfake technology, consumer trust, and regulatory oversight in sustainability marketing. Modeling firm decision-making, consumer trust evolution, and regulatory interventions as a two-period game, the research identifies threshold conditions under which deepfake campaigns yield short-term engagement benefits but ultimately risk long-term brand equity erosion. A numerical experiment simulation validates the model by showing that increased detection probabilities and trust penalties shift consumer behavior and firm strategies toward more transparent marketing. These findings provide theoretical insights and practical guidance for using deepfake technology ethically.