To sell items on GunBroker, sellers must use either VISA, MasterCard or Discover to guarantee their account. We do not accept American Express as a payment method on file for your account.
However, when making a payment on your account, you can Make a Credit Card Payment with any card (including American Express), and the card on file used to guarantee your account will not be charged as long as your payment is received prior to the 20th of the month.
For additional information, see:
Making a Payment on Your Account
Setting Up Your Account to Sell Items