I offer FLAT RATE SHIPPING and when you buy more items (same or different) from me, postage is calculated automatically for each item and so postage fee can be enormous.
But I do COMBINE postage, and will charge you the exact postage just "Request Total From Seller" before payment and your invoice will be sent with amended value with corrected postage for all your items.
Here is how you do it:
Make sure your items are in your cart. Click on the shopping cart in the top right hand corner when shopping carts opens right above the items in your cart.
On the top right side of the list of items you will see "Request Total From Seller". Click that to request the total.