What if a customer gets charged the wrong amount in duties and taxes?

The most likely culprit of discrepancies in duties and taxes is incorrect weights in your cart.  All packages are re-weighed in our processing facility, so if the package weight is vastly different than what is configured in the cart, that could cause discrepancies in the billing process. We recommend checking the weight(s) in Shopify if you feel the Duty and Tax calculation was incorrect for the product(s) purchased. 

We will be more than happy to issue a refund if the customer is charged incorrectly as a result of a Passport software issue.