Lots of people do it. I was doing it too - as a way to sell some of my Swagbucks gift cards. Selling electronic gift cards is SO easy and fast. But, it has come to my attention that they are not allowed. (Hey, I can't know everything!)
Here is the policy directly from eBay:
"You can sell most gift cards on eBay, though there are a few restrictions. This includes things like the number of gift cards you can offer at a time, the maximum dollar amount of the gift card, and the type of cards you can list. Gift card codes or electronically delivered gift cards are not allowed."
So there goes another one out the window. But you gotta play by the rules. I just checked - there are 33 active listings for Amazon electronic gift cards. I will go back to selling the Starbucks cards that are actual cards you have to mail. Click here to find out how I get $150 a month in free gift cards. Yes, it is legal!