What replies you can give if a prospect wants a discount during a sales meeting

A discount can be a powerful tool of persuasion, but it can also be an inconvenience that the business person has to be able to handle in order to avoid selling the product below cost. When used correctly, however, a discount can be a great way to push forward a slow sale or to motivate a client to purchase a higher level version of the product. But when the request for a discount comes from the prospect, do you know how to react?