1963, noun ("trick, ruse, swindle, cheat") and verb ("to trick or swindle, perpetrate a fraud"), U.S. slang, a carnival term, of unknown origin. Perhaps related to 19c. British slang scamp "cheater, swindler" (see scamp (n.)).
Entries linking to scam
scamp n.
1782, "highway robber," probably from dialectal verb scamp "to roam" (1753, perhaps from 16c.), which is shortened from scamper. By 1808 in a general sense of "fugitive, vagabond, swindler, mean villain;" used in the affectionate sense of "rascal" since 1837.