Ouvrage Collectif 
Product Funnel Optimization [PDF ebook] 

Rather than just selling individual products and/or services to customers, wouldn't you like to develop a system that allows you to provide them with an initial offer followed by additional sales of other products and/or services? It is by evaluating the needs and demands of those who have already purchased something from you that you can then often sell them many other products and/or services, usually for higher prices than that of the initial offer. By funneling other products and/or services, your sales volume and your profitability will soar!