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by gpderetta 800 days ago
Exchanges already extract per order commissions. You do not pay per message (so add, cancels and amends are free, you only pay when you get traded [1]).

A per-message would probably significantly affect existing strategies and greatly increase spreads, but I don't think it would prevent all forms of ULL trading.

[1] But even there exchanges offer rebates, if not outright incentives, for market makers to provide liquidity.