

All orders cost money. If they’re not charging you $5 per trade or whatever, then they’re taking a lot more than that by selling your “order flow” to someone who’s shaving little bits off it by creatively timing when the trades actually are going through and at what exact price.
I’m not super familiar with it, but just knowing the little bit that I know about it, this is my guess:
… and so on. I would bet it’s decently more complicated than that, but bottom line, there’s a reason these guys are paying all this money for order flows. It’s not because they’re not making money on them, and usually the procedure is to extract the money from the most-poorly-informed person involved (which in this case is the end user by a big margin).