It's good practice to have authorization to charge a client or customer's credit card written into your contract. Here is a sample template:
PAYMENT WITH DEBIT OR CREDIT CARD:
I the undersigned hereby agree to pay the indebtedness incurred by _________________ for the services rendered by Business. I hereby authorize Business to charge my credit card on file for any balance remaining on the above client’s account if not timely paid in full.
Credit Card Type:
Credit Card Number:
Name as it appears on card: