For anyone interested, there was a pretty good article about this in this months 3D World Magazine, current in the US, being number 124.
It mentioned that a court ruling in California allowed someone to sell a license of AutoCad on ebay that was purchased from a architectural firm. This is being appealed by Autodesk however.
The point being Autocad and other software are being sold as products with a set fee, which is different to being sold as a service where there is continual payment, so the subscription services for 3DSM etc would not be included in this.
Various companies allow you to transfer your product license to a new user after sale, some with more ease than others. Some packages the license can be transferred when both the old and new user get in contact, others where the seller gets in contact. Some were free to transfer, some had a transfer fee ranging from $50-200