If a customer signs up and doesn't pay but then wants to later pay by credit card, can they do that?

Yes, a customer can pay off their balance using a credit card.  

• You can enable this feature by going to Programs > Configurations and changing Enable Pay Balance to Yes.

• For a customer to pay their balance, they would do the following:
• Sign into the league web site.
• Click Order History on the left sidebar.
• The Order History page will show the Balance Due - they can edit the amount and then click the Pay Balance button.
• This will take them to the checkout page where they can enter their payment (ie. credit card) information.
• Then they click the Place Order button.