When you purchase tickets through an unverified seller (a scalper or from a classified ad), there is no way to guarantee that the tickets are authentic. Once the tickets are purchased from those sources, there is usually no way to contact the person that had sold them to you if there is any problem at the event.
With us, you have nothing to worry about. We screen all sellers that list inventory for sale, and we back our tickets with a 100% Guarantee. Our Customer Service agents are available in case you have any questions along the way, and your information is always secure.