This study examined how greenwashing message types and exposure to truth-revealing news shape consumers’ perceptions of maxim violations and advertising responses. A survey of 360 South Korean adults exposed participants to one of six greenwashing message types and measured responses before and after reading an article. The findings indicated that differences across message types were generally limited, while exposure increased perceived deceptiveness and led to negative shifts in attitudes and intentions. An interaction effect showed that exposure-related declines in attitude toward the advertisement varied by message type. Perceived environmental knowledge positively predicted all advertising responses, whereas environmental concern was associated only with eco-friendly product acceptance. Claims perceived as insufficient, irrelevant, or unclear were associated with more negative responses, with perceived inaccuracy emerging as the strongest predictor, particularly after exposure. These findings show that external information shapes both consumers’ evaluations and interpretations of environmental claims.