Shipping costs are calculated based on the cost of shipping from the supplier to your customer. The shipping cost viewed on the item detail page displays the rate from the supplier to your location, but this may vary if your customer is located in a different region.
For example, if both you and your supplier are located in the U.S. but your customer is located in Spain, the shipping cost would reflect the U.S. to Spain rate.
Similarly, if you are located in the U.K. but your both your supplier and customer are located in the U.S., the shipping cost would reflect the U.S. to U.S. domestic rate.
In general, domestic rates are priced at $5 or less. International rates are priced $15 or less.
For more detailed information on how shipping is calculated and the differences per region go here.