It have been the fourth time this have happened to me over the last few months.
I win in auction, and get an invoice with shipping charge higher than originally was in the listing.
Trying to contact
ebay was not helpful, as they stated "the best thing you can do is request to cancel the transaction ... and you can also leave the appropriate Feedback of how the seller treated you.".
The reasons the seller gave me usually are that they want to ship the coin insured/priority shipping or that they have made a mistake with the original listing.
Sometimes I feel they are just not happy with how the auction have ended, and want to compensate themselves on my behalf

.