Hi Horsa, ancient coins are a highly specialized sub-field. You will find relatively few Australians know much about them at all and the market for them here therefore will be relatively illiquid. Kind of defeats the purpose of investment right? Other valuable coins (anything over a couple of hundred) should not be bought from ebay unless you know the item inside out and the seller to boot.
This is a good australian coin forum but you wont find much discussion about ancient coins;
