Decem I looked it up for you, please read and then summarize and tell me what it means:
From Richard English: “I have just been discussing with my son the origin of the word spiv. I am well aware of the meaning of the word—my late uncle Arthur made his living depicting a loveable spiv in the 1940’s and early 1950’s—but until now I have never even thought about the origin of the word. My son, who is studying early 20th century history, claims that he had seen a suggestion that it was back-slang derived from VIPs but I thought that this acronym was more recent than WW2. In any case, I couldn’t see that a spiv was necessarily the opposite of a Very Important Person; indeed, I suspect that a spiv was a VIP to many customers during the war and just afterwards.”
Let’s put the footnotes first on this one, because spiv is a characteristically British English colloquial term whose meaning and cultural implications will be obscure to anyone outside the country.
A spiv was typically a flashily dressed man (velvet collars and lurid kipper ties) who made a living by various disreputable dealings, existing by his wits rather than holding down any job. (Another name was wide boy, with wide having the old slang sense of sharp-witted, or skilled in sharp practice.) He was a small-time crook, living on the fringes of real criminality. He is most strongly associated with the period during and immediately after the Second World War in Britain; he always seemed able to get those coveted luxury items that were unobtainable in that period of austerity except on the black market, such as nylons. Private Walker in the BBC television series Dad’s Army was a typical spiv; Arthur Daly, the second-hand car dealer in Minder, was a linear descendent of the breed.
Having explained all that, I now have to tell you that nobody knows for certain where the word comes from. Its first known use in print was in 1934: “Spiv, petty crook who will turn his hand to anything so long as it does not involve honest work”. It has indeed been said that it is VIPs backwards; also that it was a police acronym for Suspected Persons and Itinerant Vagrants. VIP does date from the same period, but it would be very surprising if it was the source. Apart from the sense being wrong, as you point out, inverted acronyms based on word play were uncommon then. The police story is just a well-meaning attempt at making sense of the matter.
The more usual explanation is that it comes from a dialect word spiving, meaning smart, or spiff, a well-dressed man. This developed into the adjective spiffy, smart or spruce, recorded from the 1850s, and into spiffed up, smartly dressed. But Jonathon Green, in The Cassell Dictionary of Slang suggests a source in the Romany spiv, a sparrow, which was used by gypsies, he says “as a derogatory reference to those who existed by picking up the leavings of their betters, criminal or legitimate”.
It’s possible, of course, that both origins are right, the one reinforcing the other. We may never know for sure, a maddening state in which to have to leave matters.