Official comment
@Dennis > The decision is up to the owner as to whether they want to sell or keep the license. The hardware is not married to the license and can be used separately. For example, the former owner may be upgrading to CDJs and a DJM, which do not come with a rekordbox dj license, in which case, he can sell the DDJ-RB without the license and then use the CDJs and DJM with it. The new owner of the DDJ-RB would have to either already have a license for rekordbox dj, or purchase one.
If the user told you they would be selling the DDJ-RB with the license, but did not deactivate and contact us to have the license unlinked from their Pioneer DJ account, unfortunately there's nothing we can do. We can't forcibly deactivate someone's license, regardless of what you tell us. How do we know he wasn't intending on keeping it and you're not just looking for a free license? We can't confirm one way or the other, so we side with the license-holder by default.
If you purchased the DDJ through eBay or used PayPal, use their dispute systems to file a complaint that the seller did not provide the full product as sold.
Sorry!