It is against our Terms of Service to sell your server or server name to another player.
If you decide you no longer want to run a server and would like to give the server name to someone else, the only way to do that is to coordinate with the other user to be available to change server names at the same time. You would need to first change your server name and have them change theirs before someone else grabs the name.
If you wish to give them your server files you can download them to your computer and then send it to the other user to upload into their server.