Let's call this purchasing initiation Forwards. The Web has enabled Reverse purchasing. Let me illustrate. A Forwards Auction involves one seller and multiple buyers. The seller determines the rules, then the potential buyers bid up the price until the highest price at closing wins the bid.
Prices move up.
The buyer determines the rules, then the potential sellers bid the price down until the lowest price at closing wins the bid. Prices move down. As an example, GM declares a reverse auction for a years worth of rubber molding.