The Featured Sellers and some others did receive a Notification that all Random listings are prohibited Starting 1st July (today).
It was a long struggle but they are prohibited now.
They already added this to the Guidelines now:
“RANDOM ITEM LISTINGS Any listing that is created without identifying the exact item that will be sold is prohibited on Gameflip. Creating listings where the Buyer has a “Random”, “Chance”, or any sort of probability of items receive will fall under this. Listings that do not identify the item to be sold will be deleted and any accounts associated with the listing may be suspended or banned.”