The answer is simple: no conflict of interrest.
I write that in a another thread:
MarketMaker are not even placing your orders on the market. Since most of the retail trader are loser, all they do is to create a virtual market, like a casino table, and replicate the market condition on it. By not placing your order on the market, when you take a lost, they win, and when you win, they start to play game against you to make you lose like requotes, frozen/disconnect plateform and wide spread... simple no?!
ECN broker, witch are not market maker, are not widening the spread to make money like MM, so they charge a very low commission instead. I think this is a fair deal/compromise to get crystal clear trading condition and stop the eternal question about: do my broker play game against me....
I use Dukascopy and you can use my IA # 2196 to get lower volume fee.
Take care