I'm assuming the seller was afraid to scare off bidders if she listed her true intentions of sucking an additional $8 from the high bidders. Whether, she wanted to recover her costs in doing business or to extract additional money for her product is totally up to her. I concider it to be legitimate as long as the buyer is aware prior to purchase.

Unfortunately, in this case the buyer was uninformed and if it was me, I would have refused to pay and would have told the seller it was excessive. If the seller was firm on the cost for shipping, I would have refused the purchase. If the seller gives a negative rating, I would have informed eBay of the practice and see if they would modify their rules in describing actual costs.