In large venue events throughout the US and Canada, why do ticket
scalpers offer to BUY your tickets just as the game is starting, or
well after the game has started, in situations where it appears far
from likely that they will ever sell the seat?  What happens to the
ticket, where does it go?  I have sold extra individual seats to
scalpers past the 1st period of a hockey game, or the 3rd inning of a
ball game, that remained empty next to me throughout the game.  You
always hear cries of "buying tickets -- any extra seats"  at the most
random events, from people who clearly have neither the intention of
going to the event themselves, nor the desire to resell your ticket. 
What gives?