Confession time - I did once abuse the Singapore system. Bought a very cheap RT ticket, checked in. Met someone who was in transit to pick up some things that my wife really needed. Then ‘fell asleep’ (was a midnight flight) to miss the flight. Made a bit of a fuss at the airline counter ‘what do you mean I can’t rebook for free’, and the RT ticket to make it less obvious what I was doing. Got away with it, but I knew it was illegal