I had posted an example a week ago on a ticket sold online and low and behold it had the information all for people to see. Now I understand that the users intention was to validate that the ticket was real but when you buy a ticket via online, you can invalidate that ticket.
What I mean by this is that anyone can use the bar code of the ticket and re-purpose it to resell. What happens is you get a duplicate ticket which is not good if your an honest person trying to get rid of tickets he or she couldn't use.
For an example of what the ticket looked like visit Things you should never buy on facebook.