Well this is what happened this week, when Gemini had a customer who market-bought the orderbook up to $2200 on BTC/USD. Shockingly and unprecedentedly, Gemini chose to reverse the trades which were purely user-error, or "fat-finger" in industry terms.
This is a grave mistake by Gemini management. Why would anyone want to provide liquidity to thicken their orderbook, when there is now a high risk of them being reversed if they are filled? This kind of policy of reversal in the event of user error serves nobody's interest but the single customer who made that mistake. It harms all the counterparties to that customer's market-buy while damaging the reputation and the expectations that bitcoin traders will have now on Gemini.
An exchange is worth nothing if it doesn't have liquidity and volume, and Gemini has struggled heavily with both. By not forcing its customers to honor their trades executed from their platform when the case involves purely the trader's error, they are incentivizing future complaints in volatile market conditions and undermining liquidity provision.
Gemini, you said you wanted to attract institutional investors, serious traders. Well, we are big boys. Forcing us to honor our trade commitment is central to holding together the integrity of the market and facilitating trust in exchanges. Your decision to reverse trades that were legitimately executed will live to haunt you in the Bitcoin exchange space.