It could be an honest mistake, but sellers are supposed to sell at the prices they list, including shipping costs.
A buyer can agree to changes in shipping cost-- sometimes a buyer who wants her purchase faster will pay a premium for an express service for example-- but she is not required to do so.
On the third hand, you can't force the seller to ship. Things 'get broken' or 'lost in the mail'.
A polite note saying that you bid based on the advertised shipping cost is sufficient.
Of course, since you won below your maximum bid, you could offer to defray the S&H if only for the karma.
If the seller goes to a Mutual Cancellation request, you can agree or ignore, in which case it ends and you get your money refunded and can leave feedback. Or you can refuse and still leave feedback.
You may have to open an Item Not Received dispute to get a refund if the seller gets snitty about this.
If you decide to leave feedback, remember that it will be most effective if calm and factual. 'Refused to ship at advertised S&H" for example.