I have used this site also. Not just for undesirable gift cards but also for store credits that are stored as a gc. For example, I had to return a few items to LLBean (shirts were literally falling apart) and since I didn't have a receipt they gave me store credit on a gc. At the time, there was nothing there I wanted to buy and needed cash more so I found the best offer at giftcardgranny.com
Sometimes the best offer is an Amazon credit and since we buy from there often, it still saved me the most in the long run. Sometimes, you just prefer a check and that's doable too.