This is more akin to financial arbitrage but my mother did a variant of this for her car payment. The card company would send her 'checks' to use for 0% balance

This is more akin to financial arbitrage but my mother did a variant of this for her car payment. The card company would send her 'checks' to use for 0% balance tansfers that she would get 5% rewards on. So she'd use the checks for her 3.9% car payment, get the rewards and pay off the card at the end of the month.