Best Place to Sell a Tmobile Prepaid Refill Card?

[beavismom]

I just bought a new phone to use with my existing T-mobile plan and it came with a $50 Prepaid Refill. It was supposed to be a physical card, but they didn't include it in the box and when I called in I was just given a code to use for the refill. I was planning to put it on Ebay when I thought it was a physical card, but I am now a bit leary of trying to sell just the code via Ebay. Does anyone know of another place that would be a good choice? I thought about Craigslist, but I don't know if anyone will trust a code without the card there either.