Keep their card on file.
View and print their invoices.
View open or unresolved issues.
Directly pay their invoice or account balance.
View their payment history and current account balance.
Update their account and contact information.
Request services… which opens a ticket in your system.
Ask a question or report a problem… which opens a ticket in your system.
Update their credit card using a validity verification before saving it (and if you auto-charge, SA can prevent your client from deleting their card on file).