This plugin is bad, and the developers should feel bad.
I really can't overemphasize how terrible this plugin has become. I've used it for years with some success but in the last six to eight months it's become essentially unusable. Do yourself a favor and check out WooCommerce, or really any other commerce plugin — using this one is the first step to failure.
The "support" for this software is embarrassing at best. Even having paid for support you can't get anyone to answer emails... ever. Take a look at their forums http://getshopped.org/forums/ you'll find that just about every topic is full of people not getting any help.
The last bug won't let people buy things! They posted an update on their blog letting everyone know that the plugin they wrote isn't compatible with the premium add-on THEY WROTE! They finally got around to making a quick patch for the error and even now no one seems to see it as being resolved, in fact the "fix" let the error continue while introducing new errors.
This is some sad, sad development. Just avoid the plugin. Move on. Save yourself the headache.