Even if you manage to earn more cash back than interest you pay, consider that cash back credit cards often have higher interest rates than cards without any benefit program. While issuers advertise their cash back cards heavily, these cards should be used only by individuals who pay the bill in full every month. Late fees also negate cash back, so never pay the bill late.

With tiered cash back, where some spending earns 1 percent, some earns 3 percent, and some earns 5 percent, issuers have become trickier. In many cases, the highest level of cash back is available only certain categories of spending, like gasoline or groceries, and the categories for which the companies make the cash back available rotate every three months. You have to pay attention if you want to keep track of how much cash back you should be earning.

If you're in a period where gasoline purchases earn 5 percent and all other purchases earn 1 percent, if you shop at a less-expensive, off-brand gasoline station to save money, you may not receive the 5 percent cash back you should. Issuers are inflexible, and customer service representatives will often say that if a retailer is not categorized correctly, there's nothing they can do to credit you the full cash back.