Torsten.

1. The Gong An say only apply for a driving license with them, other agents and companies can be scams or provide illegitimate licenses, so why take the chance?
2. How can a 'Chinese driving license with car and motorcycle entitlement' be issued in a city which has a ban on motorcycles?
3. Of course in China anything can be done with the right connections. That means your Shenzhen license may look real and pass basic scrutiny, but if there is an accident and the license is properly checked how can we know that it's going to be real? The license could be outright fake, could be issued by a real Gong An but not all the paperwork and computer entry has been done, or is real but if the Gong An Officer who has been cutting corners and providing 'back-door' licenses is caught then your license would become illegal.