A business colleague once told me of this approach (without responsibility):
He would book in a given class of service selecting a flight close to being overbooked in his chosen class. He would arrange to arrive at the check-in counter within a few nano-seconds of the cut-off, hoping that the flight had become overbooked and his seat had been given away. His dress was usually that of a senior banker and his demeanor measured, polite but very serious. Oh, he would say, but I have urgent affairs at my destination and can't miss the flight. Rather than accept the fault was his, nor the proferred compensation, he would politely, but firmly suggest an upgrade. He claimed to have had this work on many occasions!!
Believe it or not.