I can add additional shipping cost per product on Shipping Properties of the product (minus or plus).
But when I add product with shipping surcharge/discount and other product with ordinary shipping price the system still show the first shipping price in the cart. Is it the way it should work?
All products have 1 shipping method (Standard 10 USD)
One particular item has shipping discount 4 USD. (Shipping freight: -4 )
So when I add this item to the cart the shipping cost shows 6 USD. (that is OK).
But when I add another item with standard shipping methods the system still shows the 6 USD cost instead of 10 USD