We consider commercial discounts for buying based on rappels. If a uniform type discount is taken, then an unwanted paradox appears: the “buyer trick”. To avoid this paradox, two proposals are presented. Both of them observe the basic principle “to a greater order, a greater discount”. The first one is that of continuous discounts. The second consists of following a table of graded discounts. Consideramos los descuentos comerciales por compras basados en rappels. Si se plantea un descuento de tipo uniforme aparece una paradoja no deseada: el “truco del comprador”. Para eludirla se proponen dos variantes que respetan el principio básico de “a mayor pedido, mayor descuento”. La primera es la de los descuentos continuos. La segunda, la de los descuentos graduales.