I have to disagree with the above line of reasoning. The airlines make the rules. As long as you stay within those rules, if you happen to benefit it is not Fraud of any type.

I have had it happen to me in the past with fully refundable tickets bought the day of the flight. Arrive to board the flight is oversold and they need volunteers. I took the volunteer got the refund and went another day on the voucher.

I have not tried it with miles, since it is harder to get seats at the last minute using miles.

Here is why I feel it is perfectly legitamite and both parties benefit.

The airline had no qualms at all selling me a ticket for $600 to fly on a RJ from DFW-AUS (about an hour flight) at the last minute (several hours before the flight) when they knew, or had strong reason to believe the flight would be oversold. The airlines thinking is, lets get as much for that seat as we can and then we will give some poor smuck that needs the money a $200 on there $125 non-refundable ticket, and the airline actually sells that seat twice. They also know that quite a bit of the DBV's that are handed out are never used. So the airline actually intends to make $725 on a seat that was only selling for $125. I do not have any qualms with the airline making as much as they can off any given seat. There cost is negligible since they send the person that got bumped on the next flight that would have flown with an empty seat anyway. The airlines goal is to make money. My goal is to travel (within the rules) as cheaply as possible.

Is it "worth it" to plan what flights would be oversold, go to the airport and hope, and then intentionally miss the flight if it is not oversold? That is up to the individual. It also depends on which airline, there booking patterns, etc. The one it happened to me on was the DL regional carrier when they were actually at DFW and they were notorius for overbooking. COex and Pinnacle generally do not overbook a whole lot. It is totally personal preference, but I definitly do not see anything fraudulent or unethical about it. If you feel that airlines selling the same seat twice is ethical and non-fraudulent than you have to say that "booking for the bump" is also ethical and non-fraudulent. You should not have a double standard on this. Remeber, we play by THE AIRLINES rules, if they thought it was unethical they would not allow it.