a broker is nothing more than a bookie... he simply takes your bets and makes money on the spread... same thing for the exchanges... you can think of a broker as the dealer in a poker game and the exchange as the house hosting the table game... they all take their percentages... you are playing against other players, not the house or the dealer.
It's a myth bad traders which set bad SL positions use to pass the blame onto someone else.
Yes they ( banks ) know where retail stops are going to be ( in the 1000's ) and yes they hit them right before a reversal, just to play with your minds and make you make more bad decisions. Yes it annoying when that happens to me.
But it's not your broker never worry or accuse them for that.
It works both ways, if you work out where the retail SL's are likely to be well that's where you get in