Ha. Creating a layer on top of broken APIs is an thriving business. Every single carrier company has a broken API. That's why companies like aftership exist.
One example I struggled with for days recently was USPS. Not only they use xml in the url parameter, the order of the elements also matters. Unfortunately, the order in the documentation is incorrect.
Hell even Amazon's ec2 spec is confusing in some places (the boto python call parameter doesn't always match the restful call, which is less documented, leading to errors in some libraries).
One example I struggled with for days recently was USPS. Not only they use xml in the url parameter, the order of the elements also matters. Unfortunately, the order in the documentation is incorrect.