how does southwest know reservation completed?

[CupCrusher40]

I would never reuse but how do they know for free riders

[TheMiddleSeat]

Not understanding the question. 

--TheMiddleSeat

[dfwskier]

in one of three ways

1) Boarding pass is scanned at the gate - reservation used

2) Ticket holder no shows - reservation cancelled

3) Ticket holder cancels - reservation cancelled