Interpretation: Dear horrible traders, we love your commission and would not like to see you all blow up this weekend. There is a chance, if we let you trade, you would blow up so bad we would actually have to ask you for more money...which you likely don't have. Please for the love of all things good in the world, don't trade. maybe, from now on, with very, very low volatility, try to immediately buy the ask and sell the bid a few times a day. you will not lose as much, and we will make much more. thanks, but this is a win-win
Any "real" broker can do the same very well too, that's not a secret many brokers also have their own trading desks.
Yes and no. At least on futures: * Brokers are not allowed to front run your order and * All transactions must be cleared AT the exchange. Their trading desk has to follow the same rules and trade from the same data feed as everyone else.
Theoretically yes. But practically nothing will stop some guy @ brokerage firm who has access to orders of clients to copy trades of highly successful traders through his iPhone on his granny's account on massive size, which can matter pretty much, especially on less liquid markets like some stocks.
but he will always be behind you in both entry and exit, thus position will move immediately in your favor if he is moving massive size and he will get slippage on both getting in and out. So you as the trader or strategy developer has nothing to worry about.
Would be true in my case, because I basically scalp the market and almost always enter/exit with MKT orders, nobody except me and Heaven knows when and where exactly, plus EURUSD is fat enough to not bother too much about someone else to piggyback trades. But if some successful trader uses swing-trading strategy for relatively low volume stocks and enters orders in advance, that can become an issue and in this case I would be very paranoid about the broker.