[throwaway283719]

What markets is this done on? On most markets that I'm aware of, there is a fee for passive trades and a fee for aggressive trades. Sometimes the fee for a passive trade is negative (a rebate) which encourages liquidity provision, but I don't know of any market that actually charges per order, and then rebates that proportionally to the liquidity providers.

One proviso is that I've never worked on US equity markets, so if this rule is in place there then I wouldn't know about it.

[yummyfajitas]

In US markets there is a (very small) per-order fee.

There are also rolling windows and disconnections for people who go crazy with quote spam or have low fill rates.