一个广告主参与了私下竞价。 如果他们的出价不是其中最高的，会出现什么情况？

In a Private Auction (PA), the highest bidder wins the impression. If an advertiser's bid is not the highest, they will not win the impression, and the advertiser with the highest bid will secure that specific impression opportunity. This is a fundamental principle of real-time bidding environments like PAs, where competition drives the allocation of ad inventory. The advertiser will not automatically win, nor will they receive a guaranteed portion of impressions, as winning is contingent on being the top bidder. The deal will also not be automatically canceled; it simply means they didn't win that particular auction instance.