Usually sellers indicate what the shipping charge will be on the listing's page, and eBay also provides a shipping charge calculator. When neither of these are present for a listed item, the potential bidder can ask the seller what the shipping charge will be before any bid is made.
Given all of these opportunities to learn what the shipping charges will be, I confess that I never understood why so many people go ballistic over shipping charges after the purchase at eBay. If the shipping charge is of a concern, there are all sorts of ways of determining this ahead of time.
There have been several times when the shipping charge has not been stated or was unclear to me when I was purchasing a heavy item, and in all cases the seller replied promptly and politely when I asked via email.
I remember the days of shipping books to someone second class to save on the postage. (His choice, he took the risk.)
I have literally seen auctions for things worth about a dollar (regardless of the bid price) that had have shipping costs of 8 bucks or more. Just silly.
The impulse buys have disappeared for me entirely.