How Does the Concept of ‘Last Look’ Function in Some Non-Public Trading Venues?

'Last look' is an execution protocol where a liquidity provider (often a market maker) is given a final opportunity to accept or reject a trade request after the counterparty has submitted their order. This mechanism allows the liquidity provider to check if the market price has moved adversely since the order was submitted.

If the price has moved, they can reject the trade, which can be detrimental to the initiating trader and is a point of regulatory contention.