* Skeptical: This is the most direct opposite, meaning someone who is doubtful and questions things before accepting them.
* Discerning: Someone who is discerning is able to make wise judgments and see through deception.
* Astute: This implies a keen understanding and a good sense of how to assess situations and people.
* Wary: Someone who is wary is cautious and hesitant to believe things without good evidence.
* Cynical: While not always positive, a cynical person often distrusts motives and intentions, which can make them less susceptible to being tricked.
The best opposite word depends on the specific context.