I think we need to wait until seeing the site working to judge technical matters, but there are some questions:

 - Guarantee Cards: How can we ensure that these cards are from reliable sources and not stolen, hacked or reused?
 - Discount: you talked about a 30% discount but did not specify the exact level, as there are a lot of competitors such as https://purse.io, which provides discounts and reliability.
 - Escrow: How can third parties ensure that you are selling valid codes and that plaintiffs can prove that the code you sent them is not working?