I bought one. They use a unique email to buy the game for you. This email can only be tied to one account. And you can change the email password. Most likely the email account is from some company in China. Nothing to be alarmed of as long as you don't link this account and email to your credit card.

When I bought the game, the seller asked whether I wanted to add more games under the same email address. So I guess when you want to buy another game next time, it will be under a different email address. This email address is then associated with your Nintendo account. Your password for Nintendo account is only yours to know. Once the email address has been associated with your Nintendo account, it cannot be used for other Nintendo account.

Like that ka? Ok. Thank god I only bought 1 game. It is not that cheap anyways. Only slightly cheaper.