Go to Settings > Services & Fees
2. rename the Tax area "Credit Card processing fee" and add it in there.
3. add a note to your invoice that says "if you don't pay by credit card disregard the fee" (Settings > Payments)
4. If they pay you by cash or check, when you go to add the payment to the Fees area on the inspection details page, you'd delete the tax off of the invoice.
*Adding additional service fees for clients for using a credit card was illegal in the states of Colorado, Connecticut, Florida, Kansas, Maine, Massachusetts, New York, Oklahoma, and Texas at the time this article was written. Check with an attorney or on your local laws before adding this charge.*