I have seen some AA domestic flights where the First (equivalent to business class) overhead lockers are closed on boarding with signs on them stating that they are for F passengers only. Very simple to do, and really did seem to act as a deterrent.
Since reading an excellent suggestion on another forum a while ago I keep a few plastic zip ties in my hand luggage. As yet, however, I have not been brave enough to use them to fasten the zip-tags on an offender’s bag together so that the culprit cannot open it at the other end (or, indeed, in the case of a multiple offender, to zip-tie the handles of more than one bag together). However, I live in a constant state of temptation 😛
Back on the original topic – it is by no means uncommon for me to swap seats on or after boarding. However, I only do this (a) within the same class cabin and (b) after asking the flight attendants for permission.
