I've done it on ebay too. A few things...
1. check out what others sell (same brand as yours) by adding one that has bids on it to your watch list. Use that as a basis for your listing price.
2. I did that with a clothing store (expensive kids' store) and mine didn't sell that high but afterwards someone emailed me and asked if i'd sell it for 20% off face value. I refused, waited 2 months til 12/1 and listed it and it sold for 97% of face value.
3. A few I won't use, I've elected to instead use to either purchase teacher gifts or use them to buy 'fresh' gift cards for teacher gifts. I.e. I had an old navy one but the teacher like gap so I went to gap, asked for a $50 giftcard (from several families) and paid using my old navy gift card.