Sweet supports "live" shipping estimates from UPS and Fedex. If your vendor is using shipping methods that rely on UPS and Fedex for cost estimates, then the order page changes a bit as described below.
As a buyer, if you have items in your cart and you navigate to the checkout page, the checkout page will load, and then once loaded, your shipping charge estimate will update with a loader icon in place of the shipping charge. Then, once calculated, the icon would be replaced by the shipping cost.
When you change quantities of line items on the checkout page, your shipping charge estimate would be highlighted in red, a “Recalculate shipping charge” link would appear next to the shipping method name, and the “Submit” button would be disabled.
Once you click “Recalculate shipping charge”, the loader icon would replace the shipping charge, and once the charge is recalculated, the value would replace the icon and the "Submit" button would be re-enabled.
Note: This does NOT apply to flat rate shipping methods. For a flat-rate shipping method, there is no need to load shipping rates or recalculate.