Seats are for bums, not bags. I personally don't care how many tickets or reservations a person has, as far as I'm concerned, if there is somebody standing, the bag is moved off the seat (as a ticket does not entitle one to a seat, and if somebody is not sitting in a reserved seat, that seat is now available). If need be, I will move the luggage myself, as it is causing an obstruction to a seat (I'm allowed to, I'm in a uniform). If the passenger objects, they can join the luggage wherever I manage to find space for it, or the platform if they prefer. I've had plenty of arguments of the "That's my seat" variety, but never heard about any of the letters or e-mails that have threatened to be been sent, and I have the satisfaction of seeing passengers who have bought tickets sitting when they expected to stand (as I always go and find someone standing when I need to free seats).
There is nothing I find more selfish than somebody putting their bags on seats to obstruct them. Yesterday, I was on a fairly busy train travelling to pick up another train, when a family of three boarded and saw that a fourth seat was reserved at their table from the next stop. They said "Lets put all our bags on that seat and spread all over the table, it'll stop anyone else from wanting to sit there". At the next station I was delighted when a chap gets on, says "That's my seat", waited for them to move their bags, and then proceeded to get a laptop out and use some of the table!
