If my two markets are Audi Financial and the Private market, my financial instrument is my car. There is a pricing inefficiency on my financial instrument between the two markets allowing for an arbitrage opportunity. That same opportunity isn't necessarily available to another owner of a 2015 S4 that is also leasing. Their buyout from Audi may be more than the market value of their particular car and no arbitrage opportunity would exist.
"Arbitrage is the simultaneous purchase and sale of an asset to profit from a difference in the price. It is a trade that profits by exploiting the price differences of identical or similar financial instruments on different markets or in different forms."
The above definition is being satisfied by my real-life scenario. Coming full circle though, I highly doubt that opportunity is available to a majority of people that lease their vehicles. So I agree that arbitrage is not a realistic strategy that is presented in the choice of buying/leasing/financing a car but in rare instances such as mine, it can exist for a very small margin of profit that probably isn't actually worth the effort of executing.