Is that really an advantage? Fulfilment is always handled by a lot of places for the big e-retailers for returns, which is similar to what eBay needs for sellers.
How much does Staples charge for its Amazon return fulfillment where you don't even need to wrap up the item?
It is really popular: https://www.staples.ca/a/learn/amazon-returns-now-available-...
I question whether it is advantageous to use GameStop stores for this or just to piggy back on what Staples is already offering to Amazon and others for their returns? Fulfilling returns for Amazon isn't significantly different to shipping eBay orders.