Online Reverse Auctions Have Been Developed in Automotive, Healthcare and Other

Online reverse auctions have been developed in automotive, healthcare and other industries to help streamline procurement processes. How do they work?

A) Sellers post a product online with a 'buy it now' price.
B) Seller post a product online and buyers bid against each other until the seller accepts a price.
C) Buyers post their requirements with a floor price and suppliers offer increasingly higher prices for the stated quality and quantity.
D) Sellers post a product and price online and buyers accept that price.
E) Buyers post their requirements and a ceiling price, and then allow suppliers to offer increasingly lower prices for the stated quantity and quality.