You do not need to pay for shipping! When a store makes a sale, they can choose to cover the shipping rate themselves, or they will charge it to their customer. You will never have to worry about paying.
When setting up your DropCommerce account, you will need to specify the shipping rates for products. You will need to specify a flat shipping rate, for each country you ship to. You can override this shipping rate for individual products on the product editing page. The Store will be charged the shipping rate you set at the time of the order, which will be paid to you.
If you have any further questions, please feel free to contact us at [email protected]