Introduction

Everybody likes to go shopping—getting something new and shiny to play with is a great feeling. Unfortunately, shopping requires money, and nobody likes to give that up. However, in the end, people will go to work, earn money, and then go shopping anyway—whether it be to provide food to survive or things for entertainment, everybody goes shopping.

App developers can capitalize on this fact not only to provide users with cool features and apps for their devices but also to make money. One approach to making money is by asking the users to pay for the app before they can use it. Although this is very common, many users do not like the fact that they are required to spend money before getting to use the product.

Another approach is to give the app to the users for free, and then either restrict functionality until the user pays or give the user extra functionality when they pay. Either approach results in the user getting more when they pay. The app can keep giving...