You already made a duplicate thread here. The moderators will get to you when they’re back online.
I knew it was fishy but I felt safe enough with the GameFlip guarantee
For the seller dispute, the sellers will have to provide proof that they delivered the items to you, and vice versa for your buyer dispute. So submit your seller evidence and just wait for Gameflip to resolve it for you. Users do get suspended for false disputes (which in these cases are scamming).