What Should Be Done When a Voice Broker Hits a Dealer's

What should be done when a voice broker hits a dealer's price as "done" at the very instant the dealer calls "off"?

A) The deal should not be concluded and the broker should inform both counterparties accordingly.
B) The transaction should be concluded and the broker should inform both counterparties accordingly.
C) The broker should immediately inform both counterparties that the deal will have to be renegotiated.
D) The broker should decide whether the transaction is concluded or not and inform both counterparties accordingly.