ClearingHouse:
You don't say what you trade - equities, bonds, options, futures, or Forex. Those markets have different regulators and degrees of regulation.
If you are a retail trader your broker can close your account for no stated reason. However, most brokers make their money off your trading commissions and margin interest, so they normally have no reason to get rid of you.
That said, my broker is InteractiveBrokers and from time-to-time someone posts here on ET that IB has warned them that they are entering\modifying\cancelling too many orders versus the number of completed trades. If they don't correct the ratio they will have their account closed.
The Forex marketplace was basically unregulated so there was no rule against a broker taking the other side of a client's position. Some Forex firms trade against their clients and I have seen posts indicating that "bad things" seem to happen. This is is now changing due to the regulators becoming aware of the abuses.
You might search for "payment for order flow" (or orderflow) here on ET for another area of potential conflict of interest.
Jack