It is not 2011 where it is difficult to find a provider that selling well-known gift cards that you can buy from reliable sources, for example, but not limited to:

 - https://www.bitrefill.com: A reliable source that enables you to purchase most gift cards, and you can purchase bitrefill cards to stabilize the exchange rate from fluctuations.
 - https://www.coinsbee.com/: A new site but it enables you to buy cards easily.

Therefore, unless an offer contains discounts, there is no reason to buy from you.

Can you prove the sources of these cards? Or at least ensure that it is from legal sources? Is it not stolen, hacked, or from illegal sources?
Is there an escrow?