People selling MPC expansions - legit?

I've seen a lot of people selling akais MPC expansions second hand. I've bought a few 'new ones' from jrr-shop and all I received was a download link. I've never seen instructions that they need to be registered to an account like you do with maschine expansions for example. So, are people who sell 'used' MPC expansions just selling a download link and no actual license transfer etc? What's to stop them selling the same license multiple times?

Akai's sample expansions are just a download link, they don't get registered in your account, there's no serial number. I have no idea if that is a legit site. but all the 'second hand' sellers on ebay are definitely NOT authorized resellers, Akai are constantly shutting them down, but one French guy just never gives up. He often bundles my MPC Bible along with all the expansions.

Jrr is a legit online store so no worries there. Thanks for the info. Seems a pretty flimsy way for Akai to be managing their expansion sales.