Seller changed postage after bid, is this allowed?

[thirdreichcoins]

This seller changed the postage from $10 to a calculated postage, after I bid. So now its over $20. Is that allowed? Seems a bit dodgy.

http://www.ebay.com.au/itm/252040780654?_trksid=p2060353.m1431.l2649&ssPageName=STRK%3AMEBIDX%3AIT