According with an annotated edition I found on Google, "Sancho" is a term commonly used by New England mother's to upbraid bad boys, as in, "you sanch!" (Charles T. Brooks, ed., Faust [Boston: Ticknor and Fields, 1860], p. 228, n. 7. The most obvious literary referent for "Sancho" is Sancho Panza, Don Quixote's squire. More @Wikipedia
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