If you put a -2 in the "Shipping:" field to list your product with free shipping on Amazon.
By default, Amazon will set up your shipping costs based on your account settings and the weight.
You can change this using a API integrated feature called Shipping Overrides (sometimes called 'shipovers' for short).
SureDone is already built to use the feature and any shipping price that you enter in the "Shipping:" field will automatically push to Amazon, this includes the "-2" value used for Free Shipping.
You can also set up more specific shipping overrides here.