Do not expect an equivalent BTC for your cards. At least go for 20% discount if you want to get some sales. Even in purse.io you will get only like 70-80% max. You can see most of the amazon sales thread, they all are selling it for at least with 15% discount. As you can see now you can purchase card from gyft with 5 USD promotional credit, if the payment done with bitcoin then there is a 3% cashback or something. So around 8% discount from gyft if its a 100 USD card. Its just my advice, still its your choice.