Не знаю, как там в контекстной рекламе, а здесь такой аукцион: покупатель и продавец выставляют свою цену, и когда она совпадает, осуществляется покупка:
   "PLATFORM TRANSACTION PROCESS
The Platform allows Buyers to submit offers to purchase virtual currency and Sellers to submit offers to sell virtual currency. The Price for which Users offer to purchase or sell the currency is at their own discretion.
Users recognise that their offers should only be submitted after careful consideration and once submitted Users are prepared to enter into a KHS Purchase Transaction with another User. Therefore, offers made by Sellers and Buyers on the Platform represent their unconditional acceptance to be bound by an agreement as soon as the Price set in their offer matches with the Price set in an offer submitted by a Buyer or Seller, respectively. Sellers and Buyers agree that as soon as their respective offers are matched, such offers are binding and may not be withdrawn. The KHS Purchase Transactions will be completed instantaneously upon the matching of the Buyer's and Seller's offers, without prior notice to the Seller and Buyer, and will be considered to have taken place at that date and time."