For enticing new clients, vast sums of money are spent on advertising by forex brokers. You can check this fact by going on Google and typing any forex related keyword. Almost all the ads will be by forex brokers. Each click costs them around $1.
Forex brokers are free to offer any price to their clients. Most of the brokers get price quotes from the interbank market with a 1 pip or even lower spread. To this pip spread they add 2 or 3 or even more pips as the price quote to their clients. These 3 or 4 pips are the risk free profits that the brokers make for each round trip trade. You see why fx brokers are giving you free platforms and trading signals, only to make you start trading as soon as possible. Your broker will make more risk free money, the more you trade!
There is a practice used by forex brokers called Price Shading. For example, if the broker is convinced that Euro is on an uptrend and its price is going to rise, the broker will shade his price quote slightly higher to take advantage of the likely increase in Euro price.
Since, there is no central exchange to compare moment by moment prices, your broker can offer any excuse like there was sudden large order in the market or the broker feed is much faster and reflects true interbank rates .
