There are two strategies you can use in the Spot market: Static and Dynamic. Use Dynamic Seller strategy unless your administrator advised you to use Static Seller strategy.
Dynamic Seller strategy sets the unit price for all buyers, at the end of an auction, to the unit price of the last unit of bandwidth sold. It creates an artificial bidder designed to always lose at the highest possible price and for the highest possible quantity. After a round of bidding, Merkato’s Progressive Second Price auction mechanism sets the price for the winner to the price offered by the highest bidding losing bidder. With the Dynamic Seller strategy, the artificial bidder is always the highest bidding losing bidder.
(For a complete explanation, see "Merkato Auction Mechanism: The Progressive Second Price Auction.”)