Quote from Free Thinker:
it is clearly defined. every exchange has rules in writing on their website. its up to the trader to know what the rules are. 60% threshold was very generous.
I think that a lot of the debate here is disagreement over what's defined and what isn't. Clearly, the rule itself is defined, as are the guidelines, but specific bust rulings need not follow the guidelines. This becomes empirically clear when one exchange busts a trade of a certain category, while the other does not. Committees at each exchange decide how to apply the guidelines, and they don't always agree, even when confronted with the same trade price at the same time.
It seems to me that if the cutoff applied had been 10%, the OP would not have suffered any loss. That's one problem with "guidelines" instead of "rules". The rules are clearly defined, yes, but they're dictated by guidelines that are not strictly followed, and this cost the OP his/her entire account.
As I mentioned earlier, the situation is
far better than it was a few years ago, when each exchange had its own rules/guidelines, and it seemed to me that people were actually placing bustable trades on purpose; abuse of the system as such seems much more difficult now.
Numerical Guidelines
Under the new Numerical Guidelines, an execution may be found to be clearly erroneous only if the price of the transaction to buy is greater, or less in the case of a sale, then the reference price by an amount that equals or exceeds the numerical guidelines for a particular transaction category. (A mistake in entering an order or a quote, or that the firm failed to pay attention to or update a quote, may not be sufficient to determine that a transaction was clearly erroneous.)
What I find amusing about this is that these "clearly defined rules" contain an obvious misuse of "then" in place of "than". I am against "grammar policing" in online forums, but for "clearly defined" rules such as these I'd think they'd at least get the word usage correct.

Oh well, I guess we're all only human.