shopperpress is a custome shop cart theme. I installed wp-showid on it. The plugin does not play compatible with the theme. I get the plugin name and ids that don't match the post ids. I am not sure but the wp-showids may have been responsible for some odd URLS from my flyshop being indexed by google. (This is just a comment because I am not sure about it yet).
The wp-shopids works great on my www.successfulflyfishing.com site. It shows the id perfectly.