Google Checkout provides another option for digital goods sales using their Digital Delivery API. It does not include support for aggregated payments, which are often useful when selling digital goods due to the fee savings from their typical low sales price. But if you're already working with Google Checkout, as we did earlier in this book, integration with digital delivery is relatively simple.

Google Checkout's Digital Delivery arguably gives us less control over the delivery process, but does so at the benefit of simplifying development. Checkout takes care of just about all aspects of the purchase, from initiating payment to notifying the buyer with download instructions.

Digital Delivery for Checkout includes three delivery methods:

E-mail is the least recommended and most manual method. The customer will receive a confirmation page after submitting their payment. This page will let them know they should receive instructions regarding access to their purchase. We are responsible for sending these instructions when Checkout notifies us that a purchase is complete.

The key/URL method is more automatic. When the purchase is completed, the customer receives a confirmation page that includes the URL or key to access their content. This could work well for video or music downloads, in which case we could link the buyer directly to the download. We could even provide the link to our Amazon S3 storage bucket with Query String Authorization.

Another case where this method might work well is for software purchases. We could generate a software key for the buyer and this would be presented to them after they complete payment.

The final method is Description based, which is similar to e-mail, but the instruction text will be displayed at the end of their purchase, instead of a notice that instructions will be e-mailed to them. For example, perhaps the buyer is purchasing an upgrade for a video game character. The descriptive delivery method could be used to inform them that their character will be enhanced the next time they log in to the game world.

As with the rest of Google Checkout's API, all information is provided in XML format. When we generate the Checkout XML, we will include special digital delivery tags in the <item> element that corresponds to the digital purchase. This is where we include the key or URL information for that delivery method, or the instruction text for the description method.

An example <item> element for key/URL digital delivery looks like this:

<item>
   ...
   <digital-content>
     <display-disposition>OPTIMISTIC</display-disposition> 
     <description> Please go to the Help->About menu in your trial version of our software to enter the registration key.
     </description>
     <key>1456-1514-3657-2198</key>
   </digital-content>
   ...
</item>

With the other Checkout services, it allows for easy integration with Django because we can render this information dynamically using Django's template language. This also means we could track purchases and keys in a Django model with similar ease. We discussed the Google Checkout XML format at length in the first three chapters of this book. For more information on digital delivery, refer to the latest Checkout XML API documentation.