When browsing items, get shipping quotes from the Postage & Shipping menu (scroll down in the item description page):

In addition, from the Purchases (Home -> Members Area -> Buying -> Purchases) menu, the buyer can edit two shipping related options (only if the invoice is Unpaid).

Select and open an unpaid invoice:

Edit from the invoice:

• Shipping Address
• Postage Method
• and
• Apply Insurance (optional)