It boils down to their reputation, which is honestly the only thing they truly have.
If they have a reputation of leaking date afterwards nobody is going to pay in the future.
So afaik, they don't resell or give it away. They also send "proof of deletion", but how fool proof that is is another question entirely.
My local homebrew shop used to sell these. I think they stopped selling it since people used bottles which couldn't take the pressure.
What were you planning on using them for?