Response to an invitation to bid (ITB) that is unacceptable, because (1) another bid has been chosen, (2) bid fails to fall within the established competitive range, (3) absence of competitive bids invalidates the bidding exercise, (4) Invitation to bid (ITB) is readvertised, (5) irresponsibility (see responsible bidder) of the bidder voids it, or (6) collusion among bidders (see bid rigging) or some other fraud is discovered.