Careful, even if you get the card first and confirm its balance and then pay, the seller could still use a copy of the numbers on the webstore and get it mail ordered to him thus depleting your balance.

Not trying to accuse anyone specific, just wanted people to be aware it is a common trick. Where I live homeless people sell give cards on the street then run to the library and order a bunch of stuff with the card to a friends place. They then take the stuff back to the store and return it without receipt for... gift cards.

The card checks out when you call to check the balance, but when you go to spend it then it is empty.

Some gift cards even allow you to transfer the entire balance to a new card.