The defense is that this behavior is legally sanctioned front running?
How can a wholesaler guarantee the exchange price in the face of disappearing orders?
I don't think they can. Instead, the wholesaler fabricates an order at the limit of your order, then reports the sale to you.
Edit: [rate-limited] Reply to tptacek comment below:
> I can't even tell if you're talking about market or limit orders.
Can you view the context of this thread? I am talking about the explicit steps listed in the comment I first replied to. Specifically, step 3 [0].
In chollida's description the orders are limit.
Step 3 appears to be, exactly, front-running as explained in my post [1] immediately above this one.
I asked if anyone could explain how that behavior was not front-running. You responded; indicating that the behavior was according to regulation.
You claim that the wholesaler must give you the best "exchange price", but I claim that such a guarantee is generally impossible to fill (time-distance-information problem), and that in the specifics of chollida's described scenario, the wholesaler is actually front-running you by examining your unfilled (limit) order and then filling it at the limit (as in, calculus) with it's own fabricated (perhaps, synthetic, but front-ran, nonetheless) order.
If such a guarantee is generally impossible, then the wholesaler must be cheating, the law is incompetent, or, both.
[0] https://news.ycombinator.com/item?id=11668835
[1] https://news.ycombinator.com/item?id=11669193