I sometimes run sales that use a discount code. When shipping to Canada (or other countries) using Shopify shipping, it shows the full pre-discount price on the USPS First Class customs declaration. This means my customers are paying duty and VAT, etc. on the full retail price, not the price they actually paid.
Is there an option to show the price they actually paid in the 'value' column of the customs form? I don't want them getting way overcharged on taxes.
I am not sure this can be tackled directly. However, if you are using the Multi Carrier Shipping label app, then you can either show the discounted price in commercial invoice or choose to show the full price. This way, your customers are not overcharged.