I feel like most of what I read about payment for order flow is insane? Otherwise normal people will start out mainstream explainer articles by saying, like, “Robinhood sells your order to Citadel so Citadel can front-run it.” No! First of all, it is illegal to front-run your order, and the Securities and Exchange Commission does, you know, keep an eye on this stuff. Second, the wholesaler is ordinarily filling your order at a price that is better than what’s available in the public market, so “front-running”—going out and buying on the stock exchange and then turning around and selling to you at a profit—doesn’t work. Third, because retail orders are generally uninformative, the wholesaler is not rubbing its hands together being like “bwahahaha now I know that Matt Levine is buying GameStop, it will definitely go up, I must buy a ton of it before he gets any!” The whole story is widely accepted but also completely transparent nonsense.
Here is the full article, with some extra footnotes in the original.