the airline knowlingly oversells a cabin because of 'no shows' and then punishes the innocent, who turn up for their flight.
Yes, well, on a point of order, it was standard practice when I first sat in on Reservations, with a big carousel used by 6 people with a card for each flight in our sector for the next 3 months, and a telex to receive and respond to bookings.
Our process was computerised in 1973 or so, and the Supervisor Code allowed an overide to overbook usually by 5% or so, that being about 1/4 of the no-show rate. But in those days people could simply rebook a missed flight, and did.
Even with specific flight validity, high rebooking costs etc, there are still no shows and so there is still overbooking, probably - I guess - without human intervention.