Let's say I make a purchase on a credit card. Months pass, and the card is eventually paid off. For whatever reason, I am then issued a refund on one of my past purchases. What happens? Do they send me a check?
They will credit your account and it will be applied to future purchases. If the credit card is not used for several months, they will send you a check or transfer it to your bank account.
Some people on this site have actually considered sending money to the credit card company in advance, so that the amount that can be charged is temporarily inflated. Keep in mind they will eventually refund the money. Plus you will not earn interest on the refund.