Here is the scenario, you go to a concert and need an extra ticket and as always in any big event somebody aproaches and offers you a ticket, they show you a printout of an online purchased ticket and because there is no way to prove if it is real or not you buy it, As you enter the venue the usher rips it appart and sends you back out.
My question is how can we avoid something like that from happening, and don't say by not purchasing from them because that is obvious.

How do you avoid that without not purchasing the ticket? <_>

Look at it. You can probably figure out that it's fake. It's pretty easy to counterfeit those types of tickets

Give the tickets to the guy and run. It looks authentic enough.

Hate to tell you this. But buying tickets from legit vendors is the only way. And the shady looking fellow in the trench coat is far from that at best.

If you have to buy a second hand online ticket. At lest do your home work. If you can't be bothered to find out witch sites sold tickets, and the basic format of said ticket you really deserve what ever fate awaits you.

Aswell Even if your second hand online ticket is real it is plausible the shady fellow you bought it from sold more then one copy of that print out.