The story
Unknown. Attested in print from 1852 (see quotations below). Compare the noun spiff, attested from 1859, as well as spiffing (1872) and spiffed (1881), suggesting participle forms of a related verb. Compare also spiv (“a smartly-dressed criminal”), attested from the 20th century.
Etymology from Wiktionary, CC BY-SA 4.0.