If you choose our per trade rate and offer liquidity on NASDAQ, ARCA or EDGX, and enter larger orders, you can get paid to trade with us. E.G. Buy 5000 XYZ on ARCA, add liquidity, cost of $4.50, then you get a $10 rebate for a net credit of $5.50. 2250 shares would be zero net commissions if you add. (Not including reg fees). One other comment. You said, "The goal of traders (not speculators) is to achieve negative transaction costs." I thought the goal of traders was to make money. Get in and out of positions with speed, efficiency and as little market impact as possible.