Gamestop Trade-In Bonus

I'm sorry if this seems like a simple question, but how do the trade-in bonuses work at Gamestop when you trade a system in towards a new console?  Like, if I wanted to trade in my old XBOX 360 Elite for a PS4, how much would it be worth, and how do I get the trade in bonus?  Does everyone get the bonus?

Step 1. Call GameStop.
Step 2. Ask GameStop.
Problem solved.