The claimed subject matter relates to a computer-implemented architecture that can facilitate computer-assisted haggling and/or negotiation between multiple parties simultaneously. For example, various proxies associated with both buyers and sellers can be configured to negotiate with other proxies to buy or sell an item. The negotiations can be required to be progressive and during the negotiations a buyer or seller is, typically, allowed to withdraw his or her proposals. The architecture can include a registration component that can resolve concurrency and facilitate a registration of an agreement between two of the parties. The registration of an agreement can create a binding obligation between the parties after which other outstanding proposals can be terminated.