You can't use reserve prices for Dutch Auctions. Sellers start by listing a minimum price, or starting bid, and the number of items for sale. Bidders specify both a bid price and the quantity they want to buy. All winning bidders pay the same price which is the lowest successful bid. If there are more buyers than items, the earliest successful bids get the goods.
Higher bidders get the quantities they've asked for.
Bidders can refuse partial quantities.