I am trying to figure out how to set up a Paypal page. I have a merchant account, I see how to do the buttons, but can't figure out how to charge a one time shipping fee. There are only two buttons on my page, two items, but if somebody orders both of them they are charged twice because both buttons include the shipping charge. There would also be a problem if somebody ordered numerous copies of one or both. I have tried searching for an answer, but have found nothing that addresses this directly, although it can't be that uncommon.
I have Shopping Cart, so the buttons I am using are "Add To Cart"