(This post is being made on behalf of someone else.) Nominally, I'll call him Bob. Apologies if this has been brought up before, I have searched but been unable to find anything regarding this (but perhaps I am using the wrong keywords)
Bob has been using CMC and Marketmaker software for over a year now. Generally, his experience has been pretty good. However, in the past 2 days, 3 trades which were marked as EXECUTED were cancelled (without his notification) and marked as "Price is incorrect: Order cancelled"
Bob is not a full-time professional trader, but he does like to think he has at least a nominal understanding of things. Previously Bob had been led to believe that once a trade was marked as executed, it was basically solid - ie neither he nor CMC could renege on it. Apparently this isn't the case - having rung CMC, they're blaming it on a software error and refusing to honour the trades.
Anyway, this has shaken Bob's confidence in using CMC somewhat. He is extremely uncomfortable in using such a system where there is an inherent uncertainty regarding whether or not executed trades will be honoured. However, as neither of us are veterans, we thought perhaps we had unreasonable expectations founded on a lack of perspective.
So what we want to know is basically, is this sort of user-pays error 'standard practice' regarding online trading systems in general? And if so could anybody provide an explanation into why they occur, towards (we hope) providing a level of assurance that would allow us to continue to trade with confidence.
More details are available regarding the specific transactions if people are interested.