Perfect price discrimination is the term given to charging each customer as much as that customer will pay. Note that some types of price discrimination are legal and others are not. Some ways you can segment your product line and charge different prices to different subsets of your user base include: feature set, time, interface, convenience, support, flexibility, and completeness. Examples include online vs. offline versions of products, book publishers offering a hardcover and then a paperback, stores offering coupons expecting them to only be used by very price-sensitive customers, and quantity discounts.