Pricing data cannot be manipulated, particularly in the forex markets because of the mathematical relationships between all the currencies.
My personal experience with FXCM was that on 2 different occasions I had a stop that the price came within 2 pips of, and they stopped me out. I called to find out what was going on and they said it was their prices in the back room is what they go by. Afterward I checked prices on my demos with other brokers, and it matched my platform.
Several occasions I tried to execute an order and my platform would not let me get in. I called to find out what was going on, and that company puts you through the rig amoral. Finally, after 2 hours, they concluded it was my computer, and of course, it was too late.
Fine and professional? Nothing doing! I don't care how much money you got.
Stop hunting is a very common practice. In a 4 trillion dollar market it is highly unlikely that a single broker can control price on a whim. The only way a broker could do this is by manipulating their data feed, which should never happen if your broker is a registered NFA member. Also, depending on your broker the spreads may get ridiculous during news releases. So at times it may appear that your trade got stopped out, despite having the price 10-20 pips away. and as far as FXCM goes it is a fine and professional broker for only those who open standard account more than 50k !