Banks are so used to making money from me, will they be mad that now I’m the one making money?

You’re right, banks have profited from your interest payments and from charging you fees for a long time!  This is your chance to turn the tables and profit from your own credit card with them!  Despite the fact that this practice of adding authorized users is both commonplace and legal, some banks don’t love it.  The worst case scenario is that they close a credit card, cutting off your ability to sell your AU spots on the credit card.  Even if this happens (again, a worst case scenario!) this in no way affects your credit score.  The credit card’s perfect payment history will continue to appear in the cardholder’s credit file.  That said, if a particular credit card being closed would significantly affect your lifestyle, we always put your comfort first, and suggest that you not sell AU spots on that particular card.