You have the ability in your System Configuration to provide a custom message to all declined Authorize.net transactions. Instead of specific information like AVS mismatch, or expired CC, or something like that you can override those specific messages with something more generic of your choosing. To set that up for the checkout. Please navigate in your WSM dashboard to:
3. Payment & Processing Tab
4. Authorize.net Custom Decline Message:
5. Enter whatever verbiage you like in the Authorize.net Custom Decline Message field.
Now when a card is declined by Auth.net the only message they will see is "Credit Card Processing Error: We were not able to complete your transaction. Please confirm you address and credit card information."