Buying for the cash back
Earning cash back can get addictive, but the urge to spend can be dangerous. Some cardholders may end up buying more to maximize a promotion or to get a special reward. But think before swiping. If you're buying just for the sake of earning cash back, you'll be richer if you don't buy at all.
For example, if you need to charge $100 on junk to get a $25 cash-back bonus, why not just hold off and pocket the $100? Consider it paying yourself with your own cash-back rewards.
And beware of attractive sign-up bonuses that come with spending thresholds. For instance, the Blue Cash Everyday Card from American Express will give new cardholders $100 cash back after they spend $1,000 in the first three months.
"If you are able to shift your buying from one period to another to take advantage of bonuses, great," says McCracken. "But don't buy something if you don't need it just to earn a bonus."