Flying on a SE Asian carrier I used to regularly "grease" the head honcho down back $50-100 for an upgrade on a 7 hour overnight flight (success rate 90%++).
In fact it never used to get that far, as the check-in staff could usually be greased for around the same amount (success rate 75%).
In fact I knew the staff at one airport so well due to this fact that when I returned later as a line Pilot to the said airport the look on their face was priceless.