Are you using the Sell Your Item Form above?
Are you using a template that you designed earlier?
If you are using Flat Rate Shipping, which you seem to be, you would have to change the shipping cost manually every time since your items are all over the place in dimensions and weight.
If you are using Calculated Shipping, which I would suggest, then for each new item you would enter (in metric measurements) the dimensions for each item allowing for packaging.
But since each SYI form is separate from all others, although certain information is carried over, there is no way I can think of that a new listing would change existing listings.
