Recoil, you say you've not marshalled a tourney so listen to those posting here who have done so. Typical things that can happen to a tourney marshall (& I'm not talking Millenniums here, just decent level stuff within the UK) include:
Verbal abuse
Being shot by players who want you to move (rather than asking you that is!)
Threats of physical abuse - actual is very rare though luckily
Bias at later events, 'cause the player reffing when YOU play was one who thought you were unfair/biassed/cr@p etc when he was playing
Being shot because players disagreed with your calls
Being expected to be alert & on your feet from 7.30am until 6.00pm, judging up to 30 games in a day, often with no break so you just grab the burger given to you between games, & hope the organisers remember to give you enough fluids
Being paid enough to cover your expenses & give you a little beer money over, provided you don't need a Travel Inn room the night before.
I used to marshall a fair bit, everything from rental customers up to national series, but I only do so now when it's things like a self-marshalling tourney. You say that there must be people out there who WANT to marshall - well I can't really think of a single reason WHY they should, especially as you would have to be very careful about solcialising with any of the players, sponsors etc as well.