Official comment
I'll give you the same answer that all Pioneer DJ support agents will...
The license included with the hardware is not tied to the hardware; the key number on the back of the hardware is not for rekordbox dj, it's a reference key for the production teams.
When a user purchases a Pioneer DJ product which includes a license for rekordbox dj, those are two separate items bundled into one purchase; hardware and software. If the original owner then decides to sell the hardware, but keep the software, they have the right to do so. The new hardware owner can either purchase a rekordbox dj license or use the hardware with another application. If the seller intended to include the rekordbox license, but did not deactivate it, we are unable to simply remove their ownership of that serial number as we could potentially put ourselves in a situation where the buyer claims they are the new owner and sole user of that license key, but then the previous owner tries to claim they are the rightful owner as it's registered in their name, thus a he-said-she-said situation.
I'm sorry you are upset by this policy, but this has nothing to do with greed on our behalf. You can ask the seller to deactivate the license from his computer(s), and once that is done and the license is no longer locked, you can then have the ownership transferred to your name / email address where you can activate it on your computer(s).