they pretend to say that they purchased that account if you do a little Google search on the email that they'll give you, it belongs to another person that lives outside SG.
I agree. They'll sell you the account but they will not give you the account itself. So, if you have problems with your switch and need to re-download the game, either they will help you OR won't give account details. Such is my experience when I had my first Switch. It was just a total waste of money.
But from my experience with other sellers, I always ask if I can change email address and password. I've had 3 transactions like these (change email and password) and so far, all's good. It's just a matter of knowing who to deal with.