Issuers advance millions of dollars for purchases made by their customers, and they often collect billions in return. Credit cards are a huge source of revenue for issuers. When you consider all the billions of daily transactions made collectively by people who use Visa, the merchant fees, also called interchange fees, are a huge source of revenue for the credit card companies. A significant amount of card users do not pay their bills in full each month. Credit card companies approach such people with offers that start off at attractively low rates but rise rapidly with late amkes over-limit fees. Similarly, issuers screen for irrational thinking by using rewards programs. Less-educated people tend to receive credit card advertisements that promote higher rewards than those offered to more-educated individuals. These come accompanied by steeply back-loaded fees.