credit card commission
参考资料：维基百科
Many credit cards can also be used in an ATM to withdraw money against the credit limit extended to the card, but many card issuers charge interest on cash advances before they do so on purchases. The interest on cash advances is commonly charged from the date the withdrawal is made, rather than the monthly billing date. Many card issuers levy a commission for cash withdrawals, even if the ATM belongs to the same bank as the card issuer. Merchants do not offer cashback on credit card transactions because they would pay a percentage commission of the additional cash amount to their bank or merchant services provider, thereby making it uneconomical. Discover is a notable exception to the above. A customer with a Discover card may get up to $50 cash back if the merchant allows it. This amount is simply added to the card holder's cost of the transaction and no extra fees are charged as the transaction is not considered a cash advance.
Many credit card companies will also, when applying payments to a card, do so, for the matter at hand, at the end of a billing cycle, and apply those payments to everything before cash advances. For this reason, many consumers have large cash balances, which have no grace period and incur interest at a rate that is (usually) higher than the purchase rate, and will carry those balances for years, even if they pay off their statement balance each month.
