I bought a used iphone and I'm scared that the old owner would track me down?

I bought it from gamestop and since I know nothing of what the old owner of the phone is like. So can the old owner track down this phone? I haven't put in my sim card yet because i'm scared that they might track me down. Should I call gamestop & ask?

No.

The way people track phones is through the SIM card.

If you're putting YOUR SIM card into the phone, then that's it, there's no way for the previous owner to track it.

All "tracking" is done via SIM.

If you have the different sim card than the old owner has then he can't track you down

Oh my god quit worrying, someone is probably more likely to find where you live using Facebook…
I'm sure if the owner didn't already, GameStop would've factory reset it. If you're really concerned, look in the settings area, about phone, and look up your phone number. Did it come with an assigned phone number? Well then just make sure you get a different one when you go through whatever company.
Unless it's some sophisticated hacker who somehow linked the phone to another separate phone in a way that's somehow incredibly invincible to a factory reset, you're fine.
And if you're really Really worried, factory reset it yourself.

You may be tracked by find my iPhone or an app like ikeymonitor ( http://ikeymonitor.com/ ) or mobile spy. I suggest you restore the iPhone first to make sure there's no tracking app set up on the phone before you put in your sim card and start use it.