This study examined infants' sensitivity to a speaker's verbal accuracy and whether the reliability of the speaker had an effect on their selective trust. Forty-nine 18-month-old infants were exposed to a speaker who either accurately or inaccurately labeled familiar objects. Subsequently, the speaker administered a series of tasks in which infants had an opportunity to: learn a novel word, imitate the speaker's “irrational” actions, and help the speaker obtain an out-of-reach object. In contrast to infants in the accurate (reliable) condition, those in the inaccurate (unreliable) condition performed more poorly on a word-learning task and were less likely to imitate. All infants demonstrated high rates of instrumental helping behavior. These results are the first to demonstrate that infants as young as 18 months of age cannot only detect a speaker's verbal inaccuracy but also use this information to attenuate their word recognition and learning of novel actions.