If you listed your items in the correct category, you would not have to add a postage charge. Every time you sell something, because you are not posting an actual item, you leave yourself open to an 'item not received' case and a full refund to the buyer.
You have been given a link to the electronically delivered items policy where it states:
Electronically delivered items need to be listed in the Everything Else > Information Products category in the classified ad format. If the classified format isn't available on the seller's eBay site, electronically delivered items are not allowed.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
