He took the barefaced girl under his wing, taught her new tricks—and then exploited her trust in him.
1580s, "with face uncovered or shaven;" see bare (adj.) + face (n.). Thus, "unconcealed" (c.1600), and, in a bad sense, "shameless" (1670s). Cf. effrontery. The half-French bare-vis (adj.) conveyed the same sense in Middle English.
Bold; shameless; unscrupulous •Nearly always seen in barefaced lie or barefaced liar, attested from 1850 (late 1600s+)