With this option you are provided with a final price for the shipping and only need make one payment. To provide fixed price quotes we need to know what the actual shipping costs will be from past orders so it is not possible to offer on all orders.
With fixed price quotes if the total item price is different than what is in your quote my US partner will contact you to get your approval to order at the higher price before placing your order. If you choose to order at the higher price you will be responsible for paying the extra cost.
If items from your fixed price quote are out of stock and you choose to order substitutes that are larger or heavier than those that were in your quote then you will be asked to pay the extra shipping cost.
The bottom line with fixed price quotes is we take on the risk of the shipping cost being more than estimated. The downside is we can only offer fixed price quotes when we know what the shipping cost will be.