Hello,
we do not recommend users to sell their accounts. According to the updated security guidelines, the account belongs to the card with which it was used for the first time. If the account is unlinked, it can be used with another card (sometimes users have multiple boxes), but it is no longer possible to link to any other card.
Also, there will be support issues when prompted to change the password - if it is changed then the login will be attached to that first card.