This article is from the Theatre FAQ, by aku@leland.Stanford.EDU (Andrew Chia-Tso Ku) with numerous contributions by others.
These are essentially legalized scalpers and typically, as in their
ads, they offer seats in the first 12 rows of the orchestra to the
hottest shows (PHANTOM, SUNSET, BEAUTY AND THE BEAST) for a substantial
premium. You can find their postage stamp-sized ads among the theatre
ads in the Sunday New York Times.
It says right on the ticket NO RETURNS OR EXCHANGES, so you will have
a tough time getting either from a Broadway show. If the show is a
sellout, there is a slim chance that this will be allowed, but the
transaction has to be done in person. If the show you attend features
star who gets billing above the title in the advertisements, and the
star doesn't show, you *may* be eligible for a refund. Check at the
box office before the performance begins.