In the 1950s spiv was a common British slang term refering to a shady person of dubious morals who engaged in dubious business, most specifically a man selling black market goods. It might also refer to someone who had the same used-car-dealer aesthetic associated with these characters, with a trilby, a ducktail haircut, a pencil-thin mustache, a loose, cheap suit, and a flashy necktie.
Merriam-Webster online currently defines a spiv as 1. a man who lives by his wits, without regular employment, or 2. a slacker. This seems to be an accurate reflection of its current use, insofar as it is still used.