A method and system are provided that enable buyers and sellers to communicate with each other and to negotiate the purchase terms of featured merchandise in a group-buying opportunity. Sellers and buyers may use various forms of on-line group-buying mechanisms in conjunction with the negotiation features of the invention. Buyers may send various inquiries to sellers regarding merchandise offered for sale through the on-line group-buying sale. Sellers may respond to buyer questions and queries, and in some instances, sellers may communicate instructions to the on-line group-buying mechanism to alter the course of an on-line group-buying sale in progress, e.g., a further reduction in price. The method and system further provides a mechanism for calculating a demand curve based on received buyer offers and applying the demand curve to an on-line group-buying sale.