Hello there, bravolock.
Thanks for posting in the Community. I can provide information about the charging fee if a customer uses a credit card.
There are different charge rates when a customer pay using a credit card. You can check the list I've attached below about the three different conditions for the fees:
To determine how much is the fee, you visit the link: QuickBooks Payments.
Please remember I'm here anytime you have questions about QuickBooks payments. You can reach out to the Community team anytime you need help.