Not only do QF have to trade in a fair and honest manner, they must be seen to trade in a fair and honest manner. If they were to put money over the bar it would appear that they are reciprocating for services rendered.
I had heard numerous rumours about AN giving FOC tickets to Air Traffic Controllers and about six months before AN's collapse, I had an ATC person visit the flight deck on a flight to SIN. At one stage of the conversation he lamented the fact that AN were no longer giving them FOC tickets. It explains why AN used to get "right of way" whilst taxying at Australian airports (& HKG).