I've been to several 7-11s in the Portland, OR area that don't sell gas and they all code as gas stations. I've never had problems buying GCs with a credit card there either.

Caution on Ebay though--you can't use GCs to buy any other GCs or anything classified as coins, paper money, or bullion. I was sitting on $1000 in GCs for 8 months after I missed that change in the T&C, though I eventually used them on a camera.