First off all, get your answers from an american because our laws must be different than a foreigners.
1. You are a minor. You can not be held legally responsible for any debt before the age of 18.
2. $900 is not a lot of money. Paypal has bigger fish to fry.
3. They can not send debt collectors after anyone under the age of 18. It's illegal and a debt collector would not take their case.
4. Delete your card, (or call them up and tell them to block any charges from paypal,) Most car companies will block charges for free if its a good company.
5. On second thought if you are a minor, how do you have a credit card? If it is your parents card it's different.
6. If you call paypal up right after a dispute and say, before selling my virtual good I alerted the customer of paypals policy on virtual goods and made them aware there are nor refunds. If you are nice and polite you will win every single time.
In my whole life I have never lost a paypal dispute. Just be polite.
I do have multiple accounts. One that has a Paypal card on it, no banking info or credit card but I can go to an ATM and withdraw immediately, another account with my bank account to withdraw money, and a few accounts with fake names. I usually move the money to a different account right after a sale, and then to my account with my banking info to immediately withdraw.
Sometimes I even move it through a family members verified account, and then to my main account to withdraw.