Google Checkout was awful to work with. It was hard for the vendor to setup and use. It was hard to program against. It was hard for the customer to use. It was

Google Checkout was awful to work with. It was hard for the vendor to setup and use. It was hard to program against. It was hard for the customer to use. It was hard to test. And of course it had Google's famous lack of support. Speaking of support, we qualified for the integration reward ($1500 or so; maybe more). We tried to claim the reward for over a year. Every time they'd say "yeah you totally qualify!" and we'd ask how to claim the reward and then silence. Of course every email response took 3-7 days. A few months later we'd go through the same process. Still waiting on that check to arrive. We supported it for about a year and eventually gave up. Payment notifications could take up to a minute to arrive. You couldn't specify the tax (or shipping from what I remember) for an order in any sane way. For a while it was over 50% of our support tickets while being used by less than 10% of our customers and less than 1% of all transactions. I was so happy to delete it from our codebase. And we won't support any payment processor they have to offer anytime soon.