Well they can do Steam though only in $20 or $50 codes that print out on the receipt. It's also available on the website which you can use trade credit to pay with.
Just show them this "Take Your Rewards Program To The Next Level
Level up & become a Pro today for only $14.99 per year. The new GameStop Pro starts June 27th at $25 per year."
On this page https://www.gamestop.com/poweruprewards/
Same upgraded my pre-order to the CE, got the zelda case and amiibo also. Traded in Sekiro and The Last of Us Part II and got $26.40 for each. Also they were offering half off the gamestop warranty on the game.
I got offered to upgrade to the Zelda TOTK CE at my local gamestop, guess I'll trade some stuff in lol. I think they called the people that pre-ordered the Zelda switch in-store. Since I got mine from that same store, and did a pre-order on the game to get the 20% boost.