On its Google Checkout page, Google claims a "Checkout" icon can increase ad click-through by 10%. (At least one client, Fred Lerner of e-commerce network Ritz Interactive, claims the Checkout icon increased clickthroughs by 23%.)

What's more, Google Checkout users purportedly convert 40% more than shoppers that haven't used Checkout in the past.

Google Checkout is a payment service styled after PayPal, but enhanced with Google's clout: AdWords clients that use Checkout can get their Checkout transactions processed for free.

They also get more visibility in Google's search results, simply because the Checkout icon is so prominent, according to Blogoscoped, which posted imagery of a Checkout-infused ad in the following Google search:

Google Checkout charges non-Adwords merchants 2% plus $0.20 per transaction. AdWords clients may use the service at no cost for sales of up to 10 times their monthly AdWords spend; after exceeding that limit, they are charged 2% plus $0.20 per transaction.

In June 2008, the WebGuild took issue with Google Checkout for not making its transaction fees more transparent to users. At the time, Google's rate chart did not specify charges for non-AdWords merchants. It also didn't, and still doesn't, reveal it charges an additional $0.20 for canceled orders.