You do not pay interest on a card with a $0 balance, as long as you don't let it cycle a month. If you carry a balance, you pay interest the second you charge something, as it goes by your average balance. I have never heard of the "waive the interest" thing, but it makes sense, as many states have laws that you would think would prevent interest from being collected in that manner. As for your credit rating, it is usually best for your credit rating to have high credit limits, no debt, and no late claims. I have read many people say the best way to increase your rating is to apply for a card, then cut it up upon receipt, so you are not tempted to use it...if you ever need it, they will always reissue it. I am not an expert on how teams operate, but I think it would be wise for them to give a credit of 101-105% of what they paid, depending on money spent and/or how long they've been a season ticket holder, or an immediate refund on 10/8.