From Ross-Tech Wiki

3.10 Can I sell my VAG-COM System to someone else?
You can sell the Interface, but the software license and support are not transferable.
If you have a "dumb" interface and the purchaser wants the full-function version, he will have to register as a new user for $99.
All of our Current Interfaces act as "dongles" for VAG-COM, so the software should be fully functional on any PC that meets our requirements. However, we only provide support to the original purchaser. If you purchase a second-hand "dongle" Interface and want to be a "registered user" and get technical support, you'll still need to pay $99 to register. 2nd hand owners of Ross-Tech Interfaces are not eligible for any of our Trade-In offers.