In the event that trades are executed at rates not actually offered by FXCM's liquidity providers, FXCM reserves the right to reverse such trades, as they are not considered valid trades. (fxcm.com)
Not only do you reconcile the «trade with a positive expectation'to «only risk what you are comfortable with losing», but also provide recent, real world examples of perfectly valid trading set ups that were losers. (learntotradethemarket.com)
The bots were capable of taking advantage of a bug on the Mt. Gox exchange that made it appear as if they were performing valid trades with lots of bitcoin that didn't really exist. (gizmodo.com)