Can I refund a customer's service deposit that was paid by check to their bank account via ACH? Is there a QB fee for this?

Yes, you can refund the customer's service deposit via ACH, sola.

Refunding a customer's service deposit via ACH may incur a fee. If you need to know how much the fee for a refund transaction, I'd suggest getting in touch with our Merchant Services Support so they can discuss with you the rates accordingly.

After that, we can refund the customer by recording a refund receipt in QuickBooks Online. See the steps below:

1. Click + New in the left panel and choose Refund Receipt.
   
2. Select the customer's name.
3. Enter the necessary information for the refund.
4. On the Payment method, select the card you'll be using for the ACH transaction.
5. Hit Save and close.
   

We can bookmark the following links below. We can learn more about the types of processing fee rates as well as steps to void a transaction:

Understand fees for refunds or void transactions.
Void or refund transactions in QuickBooks Payments.

Feel free to get back to the Community space if there's anything else you need aside from refunding a customer or any ACH concerns, sola. We'll be right here to help. Have a good day!