Is stub hub a reliable source?

I purchased tickets through Stub Hub, after seeing my friend purchase tickets from stub hub for lady gaga and said everything went great. I purchased tickets for katy perry at the bank atlantic center. I received my tickets, but instead of regular tickets, I received tickets that are printed off someones computer. I am now imagining that the seller is printing and selling these tickets over and over again, and I'll get to my concert and find out I don't really have valid tickets. I know I can get my money refunded by Stub Hub if that happens, but that won't help me as I stand outside the venue, crying that I can't get in to see Katy Perry.I checked the website before and they have the fan protect guarantee thingy but you can never be sure Should I be concerned, or do I just have an overactive imagination?