Because SeatGeek's marketplace is meant to connect users with ticket sellers, we give sellers a great deal of freedom in how they list their tickets. As a result, we allow sellers to specify the number of tickets that can be sold from a given listing.
In most cases, sellers will set up their listings so that they won’t be left with a single ticket since they're generally harder to sell. For instance, a listing of 3 tickets may allow you to purchase 1 ticket or 3 tickets, but not 2 tickets.
Our event pages include a feature that allows you to filter listings by the number of tickets available. That should make finding a particular quantity of tickets much easier.