1. that can be duped

suspicious cynical untrusting worldly astute discerning knowledgeable perceptive sophisticated unbelieving wise sharp shrewd insightful discriminating clever intelligent judicious acute smart protected unexploitable guarded safe secure strong impenetrable inaccessible locked sealed tamper-proof clear-eyed clear-sighted critical hardheaded mistrustful sceptical(UK) skeptical(US) wary careful cautious suspect apprehensive cagey distrustful doubting dubious suspecting vigilant watchful circumspect doubtful hesitant stubborn unaccommodating uncompromising unyielding difficile steadfast obdurate unflinching unmanageable unpermissive unrelenting argumentative disobliging fussy headstrong inflexible intransigent obstinate particular picky