You can't buy someone else's fitness card. Because the fitness card is not a simple card, the personal information of the user is bound on the card. Every time you use it, you will check whether the user's information is consistent with yourself. It can only be used if it is consistent, but it can't be used if it is inconsistent. So it is best to handle the transfer and update it to new users. Therefore, you can't buy someone else's fitness card.