We understand from the passage that the work a check-in clerk does ----.

The job of check-in clerks at any airport is not a
particularly interesting or satisfying one. They simply
have to check the tickets of passengers, and take
their luggage. The work is mechanical, repetitive and
very tiring. The only variation in the routine occurs
when things go wrong ñwhen flights are delayed or
when they are cancelled due to such things as bad
weather, strikes or technical problems. Then the
check-in clerks are in the unfortunate position of
having to face the angry passengers though the fault
is not theirs and they can do nothing to put things
right.