My client has items for which they charge a flat rate for shipping. They put the items in Priority Mail boxes or envelopes and always charge the Priority Mail price as the only option. This is easier for the client than calculating the shipping cost individually for each customer.
A problem arises when the customer wants to order more than one item, even if the item is basically a piece of paper and when multiple units of the item can go in the same envelope. If the customer orders two units of the same product, they are charged the flat rate for the shipping twice.
Any suggestion of how we could work it out so that they could purchase several units of an item for the same flat-rate shipping cost?