Question

Mary is an authorized user on her parents' credit card. What may happen if Mary doesn't use the card in a responsible way?

Answer 1

The answer is:  Mary and Mary's parents' credit may be damaged

Even though Mary is an authorized user of the card, the credit history from the credit card that Mary use is still tied to her parent's name.

This mean that if Mary do fiscally irresponsible behavior such as maxing out the credit cards, or keep losing it, her parents' credit score would plummet and it would be hard for them to obtain loans in the future.

Answer 2

 If Mary doesn't use the card in a responsible way, there's a possibility that Mary will spend more than what her parents allowed her to spend. Therefore, giving more payment duties to her parents which could also result to debt if the amount spend is too much.