"petty crook who will turn his hand to anything so long as it does not involve honest work," 1934, British slang, probably dating back to late 19c. and connected with spiff (see spiffy) in one of its various senses. Being a flashy dresser was a spiv characteristic.
The spiv reached his apotheosis during World War II and the succeeding years, when the disrupted economic conditions allowed ample scope for unofficial trading (a pair of nylons here, a few packets of cigarettes there) and other petty crime. He became a stock figure in the English social comedy, represented on screen by such stereotypes as 'Flash Harry' (played by George Cole) in the St. Trinian's films and Pte. Walker in Dad's Army. [Ayto, "20th Century Words"]
late 14c., magike, "art of influencing or predicting events and producing marvels using hidden natural forces," also "supernatural art," especially the art of controlling the actions of spiritual or superhuman beings; from Old French magique "magic; magical," from Late Latin magice "sorcery, magic," from Greek magike (presumably with tekhnē "art"), fem. of magikos "magical," from magos "one of the members of the learned and priestly class," from Old Persian magush, which is possibly from PIE root *magh- "to be able, have power."
The transferred sense of "legerdemain, optical illusion, etc." is from 1811. It displaced Old English wiccecræft (see witch); also drycræft, from dry "magician," from Irish drui "priest, magician" (see Druid). Natural magic in the Middle Ages was that which did not involve the agency of personal spirits; it was considered more or less legitimate, not sinful, and involved much that would be explained scientifically as the manipulation of natural forces.