The reality is that flights rarely leave these days without being full. As such, the only way to ensure an empty seat next to you is to buy the additional seat.



However, one thing that has worked for me on WN...although with a big risk of backfire..is to pick an aisle seat next to a COS in the window. That COS keeps people from sitting in the middle seat, but the seat prevents the COS's body from spilling into my space. This will only work on flights you KNOW are not full.