After an authorized user (AU) is on-boarded to your tradeline for several months and they have seen their credit score rise, you remove them as an AU and a check is directly deposited to you.
Seems like a situation where identity theft can happen, however you know the identity of your AU, but they don’t know who you are. In other words, an AU cannot disappear on you or spend all your money, because when you use a company acting as the clearinghouse there is separation.
The AU will not receive a credit card and is not allowed to spend any money on your account. The card will only be sent to the primary account holder’s address (you) and many banks even allow the option of checking a box so that a card is not even issued at all. Additional security measures can be taken by setting up alerts on your accounts and phone passwords to be extra safe.