I read the IATA article as :"Fines [to the airline] average out at $3,500 per passenger, and airlines then have to fly the incorrectly documented traveller back to their country of origin at their own expense." So the Airline gets the fine and cost of returning the passenger. Obviously they will try and recoup that from the passenger by all means possible. One could argue that if all documentation is in order, and was validated by the airline, it is not the passenger's fault for not being admitted however, there is always a reason for refusing entry and the airline could argue in almost any case the passenger is responsible. Especially from the hours I spent wasted watching 'Border Security'. The most frequent examples are people trying to enter a country as a tourist and immigration suspects/confirms they are trying to move for employment /permanently, or having a criminal record. The time where someone is turned back for no real/valid reason must be very rare and hard to prove to the airline.