Selling game keys/ giftcards

Is it possible to sell a key/giftcard and get scammed? I’ve sold an ITunes card before, and it went perfect. Today, I’ve gained suspicion because I’ve listed two Xbox Gold Live codes, which have been half-way sold (purchased, but the other person has not rated me). It it possible for the other person to use the code and not rate me, getting me scammed? Thanks.

There’s the gameflip’s system, where they have three days to rate you, if time runs out, the transaction will be automatically finalized.

Thanks! Made me scared, but I’m glad Gameflip has that.