its safer than buying stuff in the actual retail store where the employee actually handles your credit card when you hand it over to pay.
account info is stored securely with apple, and you just enter your account login/password to make purchases from then on.
If you are really paranoid, the best security would to take cash to a local store and pick up and iTunes store gift card.
enter the gift card info into iTunes and your account is then credited with however much you put on the gift card.