Old problem. I wrote about it many times here and that’s a reason I never buy and don’t support sellers of digital game codes that don’t sell as instant delivery.
It’s a safe and unfair business. Every seller can list bunch of games, even AAA titles, waiting for someone to bite, and then buy it elsewhere for cheaper before delivering. It’s good practice for them, but bad for this site and other sellers. It’s bad for the site, because nobody will come back to buy more from Gameflip after such a bad experience. For other sellers is bad, because it’s easy to spam over our listings with something they don’t have. They can even offer better price for something if there is no risk of loosing money (they will never spend on a game if nobody buys it).
That’s why I’m still standing behind my suggestion to prevent this type of things by limiting every user to have max 5 non-instant (digital) items at the time.