Why is that distateful? My impression is selling flow is the only way for retail brokers to keep competitive prices while complying with SEC rules. Instead of executing orders themselves according to the rules, they sell the order then price it to the customer as if it had been executed by the rules. I've never worked in equities so correct me if I'm wrong.
My concern is that the investor doesn't understand what is happening. Someone goes out to hit a bid, but actually a prop group has paid to see their intention before it goes to the market, and can choose to participate or not.
But I'm a futures guy, so my understanding of payment for flow is minimal.
