How do children use informant niceness, meanness, and expertise when choosing between informant claims and crediting informants with knowledge? In Experiment 1, preschoolers met two experts providing conflicting claims for which only one had relevant expertise. Five-year-olds endorsed the relevant expert's claim and credited him with knowledge more often than 3-year-olds. In Experiment 2, niceness/meanness information was added. Although children most strongly preferred the nice relevant expert, the children often chose the nice irrelevant expert when the relevant one was mean. In Experiment 3, a mean expert was paired with a nice non-expert. Although this nice informant had no expertise, preschoolers continued to endorse his claims and credit him with knowledge. Also noteworthy, children in all three experiments seemed to struggle more to choose the relevant expert's claim than to credit him with knowledge. Together, these experiments demonstrate that niceness/meanness information can powerfully influence how children evaluate informants. (Contains 5 figures, 2 tables, and 6 footnotes.)