美国股市交易量越来越多的被送到Citadel这样的做市商而不是交易所。这对Price Discovery十分不利。The level of over-the-counter (OTC) U.S. equity trades has hit a record-high 44.1% of total shares, mostly driven by retail investors. Orders from that group are sent (mostly sold) to wholesalers that executed them off-exchange. While this may not sound advantageous to retail investors, the majority of these orders are executed at better prices than what's displayed by exchanges. This process is called wholesaling. The term used to address how compensation is directed for trading is called payment for order flow.