1. the guy selling the bike got his money 59 seconds sooner, is this not a benefit? 2. Anybody who wants can buy the premium service. That means there may be multiple people competing for the $100 spread between the buyer and seller. In your scenario, they have all posted adds selling a bike for $599, but only one can buy the bike for $500, and the rest have to buy the next highest priced bike if someone accepts their ad. Some of them may not make any money or may lose money on the transaction. Therefore, in order to prevent this, the next time they will offer a bit more than $500 to the seller, to make it more likely that their buy offer is accepted.The trade still happens more quickly, the seller gets more money, and the HFT guy gets a smaller profit. Over many trades, the competition reduces the HFT traders profit, while still speeding up the rate that bikes are bought and sold.