Whats the truth about online books limiting/banning winners

I'm in my sophomore year of sports betting and after much trial and error I've got what appears to be a very lucrative system on my hands. Frankly the only concern I have at this point is this whole thing I keep reading about online books restricting winning players. .. Is this really an issue and at what point do I become liable to get shut down. I'm only up a few thousand at the moment. 

I use BookMaker - am on the run of my life.  Currently up $140K over the last 6 months, and haven't been restricted in any way.