A store differentiating shipping per product with one free-shipping item

When a store sells mixed-weight products under one shipping price, it pays for that simplicity from its margin: the light accessory carries a cost it never deserved and repels its buyer, while the heavy product ships below cost and eats the profit. Promotional campaigns compound it when the merchant wants free shipping on one product without extending it to the whole cart. Product-level rules solve that equation precisely.

Shipping rules are added at the product level: free shipping for a product or a product-specific price. At checkout the rules apply according to the store cart shipping calculation mode: the largest line price, the sum of prices, or the table price with a single free-shipping product exception. Calculation happens on the server from product data plus the merchant table together, never trusting browser values.

In practice, identify your heavy products first and give them a special shipping price reflecting true cost, and pick a single promotional product for free shipping instead of a blanket offer. Choose the calculation mode fitting your typical shopper cart: the largest for mixed carts, the sum for multiple heavy orders. Test mixed carts before the campaign to confirm the expected total.

Among the limits worth knowing, product shipping rules apply through the store cart shipping calculation mode rather than as fully independent pricing apart from the general table. Understand how rules interact with the zones table first, and review the linked shipping-zones scenario before designing a complex structure.