Abstract: A method for offering for sale of a product, the method being performed under the control of a first computer system connected to a computer network, the method comprising collecting, via the computer network, information from a plurality of potential purchasers of the product, the information including for each of the potential purchasers: identification data identifying the purchaser; purchase-condition influencing the conditions under which the product is going to be offered to the purchaser; defining at least two groups of potential purchasers; the purchasers in each group having at least one purchase-condition influencing data in common; generating, based at least on said common purchase-condition influencing data of each of the groups, at least one condition under which the product is offered for sale to the potential purchasers of each group; forwarding information containing said at least one condition to each of the potential purchasers.