I don't think you can. You might be able to trade it for a different one if it's defective. You might be able to start yelling at the manager or something. What does it say on the receipt?
The White Vita is hard to come by and fairly sought after.
$170 for a used does not sound like a good deal. You can get the Walking Dead bundle for $199 msrp. Therefore, Black Friday deals will probably be down to at least $170 and probably less, for a new one.
I'm generally pretty good at taking care of my money, but I'm also one of those weak-willed pieces of **** who (sometimes) asks others for help and trusts (some of) my fellow human beings. It's sad, I know.