[oangemangut]

In the case of Dark Pools, it would actually be the crier saying "a lot 10x the size of what I'm auctioning just traded somewhere else where none of you lot can trade for xx price". So after they say that you actually do know the price that they bought the item(s). This is since the dark pools have requirements to report to the trade tapes their trades in fairly similar latency to the exchanges themselves.

EDIT: The rules also dictate the allowed prices the dark pools trade at. They have to be within the national BBO, they can't just trade at whatever price they want. So the public auction is actually helping them find the prices, without their pre-trade information affecting the price before execution.