I think you just hit the nail on the head. Everyone has an incentive to sell/pass on fakes and it's the end customer who pays. Stockx/Goat have huge incentives to pass on fakes or just not give a F because they get commissions from it. Unless the shoes are so obviously flawed, they can just pass it on real and no one can claim otherwise. These businesses have been great at fooling the end consumer, they're basically saying "it's real because we say it's real".
The thing with stockx and Goat is, they could easily dispell rumours of fakes by insisting people include receipts when selling their shoes. But why don't they do this? Because they want the power and control in the authentication process. I'll bet there would be a lot less shoes going around the resale market if everyone insisted on receipts.
How do you want people to claim and prove they're fake though? Reps are made very close to 1:1 these days, if not already 1:1. Any discrepancies can be dismissed as factory flaws. The only difference between zadeh and others is that zadeh hasn't been caught yet:
Here's how one former med student started a successful fake operation on Reddit from the comfort of his own home.
www.vice.com
And how or where does he get them wholesale for $110?
Rep forums on reddit haven't been shut down. Rep factories in China haven't been shut down. In fact the reps market is booming, so who is buying all these reps I wonder.