Besides your subscription charge, Adobe does not charge you transaction fees / service charges when you use forms with payment enabled. However, PayPal does charge you a transaction fees (please check PayPal web site for details.)
How does the payment method work on credit card work then? Does it go to direct deposit?
After filling out the form and then submitting, you will be then redirected to the PayPal page to complete your payment transaction. How will you be charged? It depends on how you set up your account with PayPal and which payment method you select at that point (please check the PayPal website for more information, you need to have an active account with PayPal before you can use payment in your forms).
For more information on how to set up your form with PayPal integreation, please check:
Additionally, you can check the forum for FormsCentral Payment: