How reliable brokers are?

 
I've never worked with real money with a broker since I've started my career in forex market. I know broker's profit is gained from traders losses.
So...I'm wondering, if I could turn 100$ to 5M $ in a month, would broker pay me?? Have you seen any case like this, which a broker deny paying a trader? Are they really reliable?
 
Robert hofer: I know broker's profit is gained from traders losses.

Only with dealing desk brokers.

 
William Roeder:

Only with dealing desk brokers.

Thanks, can you please explain more?
 
Robert hofer:
Thanks, can you please explain more?
My beloved aunt Google is always willing to explain in almost any language you prefer dealing desk brokers and  ECN / STP brokers.