I say if you're selling the website, download all the files and a backup of the sql databases (if any), zip them up into a rar, and transfer -that- to your customer.
Won't involve you possibly getting on the wrong side of the TOS, because you're still the only one accessing your account - they'd have to get their own somewhere to put the files on, but it's one way to do this if the uppers say it's against TOS to sell your x10 account altogether