Enable your customers to choose lettermail shipping, but don't overcharge if they buy card + product
Are your customers abandoning cart when they see high shipping costs for lightweight items? But adding a lettermail category causes Shopify to overcharge for parcel shipments - it charges the lettermail cost in addition to the parcel cost. FixShip - Lettermail is a simple little app that enables products to be tagged for lettermail. It displays the lettermail pricing only if all products have the tag; otherwise it hides the lettermail option and charges only for parcel according to your rules.
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