Overbooking was the practice of selling seats to more passengers than there were spaces to be had on a vessel. It was considered an acceptable Ferengi transit practice.
In 2370, acting as a broker, Quark "slightly" overbooked the evacuation vessels he had sold tickets for in relation to Deep Space 9's evacuation. This caused a situation near the airlocks, necessitating Commander Benjamin Sisko's intervention. Quark tried to defend himself, citing his people's acceptance of this as normal business practices, and added that he felt sure that Sisko could handle the situation. Ironically, he was left without a seat of his own, as Rom had sold his. (DS9: "The Siege")