I am sorry to say but after reading many blogs the Shopp seemed the best alternative for a wordpress shop website and the reality was not so perfect. The company building the software is not offering acces to the forum before buying a license, because if you read the stuff in there you will never want to buy the software. I am angry because I have spent money and time to debug the application and the huge bugs are a show stopper.
The integration with wordpress is not that ok, think that you can not use WordPress search to search inside the wordpress pages and post at the same time to the products inside the shopp. The custom types used in the shopp plugin have noting to do with the ones in wordpress so any special implementation requires core modification.
Orders are not registered at the submission of a form, but after the response of the payment gateway and many other problems like this.
The worst part is that the support for this pluggin reassembles more of a hobby for the developers. The forum community is nice but not so helpful, there are a lot of post without answer and some of them describing serious bugs.
I am using the last version 1.1.5 and we have 2 experienced PHP programmers working on the project.