It's important to present your rates clearly to customers — ideally in chart form. Reward customers who purchase more by lowering shipping and handling charges for large orders.
Customers expect to pay shipping when buying direct, but they don't always understand handling. If the mail order purchase price grows significantly higher than purchasing the same item in a store, you're likely to lose the sale. Find a middle ground that leaves you with a cushion while still pricing your products competitively. After you've gathered some selling history, you'll probably want to revise your rates appropriately.