While the academic definition of arbitrage requires it to be risk-free, in practice there is always risk of some form. If you're buying gold in SF for $100 and

While the academic definition of arbitrage requires it to be risk-free, in practice there is always risk of some form. If you're buying gold in SF for $100 and selling it in NYC for $101, you carry the risk that the price will move while you're executing the trade. If you're doing the yen carry trade (borrowing yen, and lending dollars), you carry the currency risk. If you're taking 0% credit card loans and buying CDs, you carry the default risk on the CDs (mitigated, of course, by the FDIC). That said, I agree with your general point - buying gold with a 0% loan carries so much risk that it's really just a leveraged investment, not an arb opp.