I suspect that the auction you listed for the number plate that started at 99cents with the first bid last Saturday, originally had a "buy it now" price. BIN's on auctions are not a reserve and disappear as soon as the first bid is placed.

You can cancel the bid, but you'll probably get a neg feedback and that will put your selling career in jeopardy .

https://www.ebay.com.au/help/selling/getting-paid/sellers-can-cancel-order?id=4136

Edit. G'day Sandy and SLR, reckon I need a coffee now................