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Build a .NET App for Google Checkout

by Martin Omander

Google Checkout is a new service designed to make online shopping faster, safer, and more convenient by integrating with sites to help people pay for goods and services online. In this article, I'll explain how Google Checkout works, give you an overview of its API, and then show you how to develop an application for it using .NET. I've also included sample code for the application. (Full disclosure: I work for Google, where I help large merchants integrate with Google Checkout.)

To start, let's take Google Checkout for a spin. is one of the merchants that have integrated with Checkout. If you go to's website, put an item in your shopping basket, and click the Checkout link, you will see two ways of completing the purchase (Figure 1). You can either use's regular checkout process, or you can use Google's Checkout.

Figure 1
Figure 1: Google Checkout, integrated with

If you click the Google Checkout button, you are taken to Google's website, where you can either log in or create a Google account (Figure 2). Once you have logged in, you can choose your shipping method, shipping address, and which credit card to pay with. Finally, as shown in Figure 3, you are asked to confirm your selections and place the order.

Figure 2
Figure 2: Google Checkout

Figure 3
Figure 3: Placing an order with Google Checkout

In other words, Google Checkout is an alternative checkout process, not a form of payment. Once a customer has created a Google account, she doesn't have to keep filling in credit card numbers and addresses on different merchants' websites, because Google has that information on file. She also doesn't have to remember login details for dozens of different merchant websites. And her credit card number is safer because Google doesn't share it with merchants.

What's in It for the Merchant?

First of all, merchants who offer Checkout get a Checkout shopping cart symbol in their AdWords ads (Figure 4). This symbol, and customers' knowledge of how fast and secure Checkout is, is designed to result in a higher conversion rate and more repeat business.

Figure 4
Figure 4: The Google Checkout shopping cart symbol

As I was writing this article, Google announced that there will be no processing fees for merchants during all of 2007. On January 1, 2008, Google will start charging a transaction fee of 2 percent plus 20 cents per transaction. But if the merchant is using AdWords, he will get $10 worth of sales processed for free for every $1 he spends on AdWords. For example, if the merchant is spending $1,000 on AdWords per month, he will get the first $10,000 worth of Checkout orders processed for free every month.

Finally, merchants using Checkout will be protected by Google's fraud prevention efforts. Google's fraud prevention tools stop invalid orders from reaching the merchant. And Google's Payment Guarantee policy helps protect merchants from chargebacks.

This article is about technology and not marketing, so I won't go into more detail here. Anyone who wants more business info about Checkout from a merchant's point of view can go to

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