Nothing beats a signed "no surprises" contract spelling out the total charges including all taxes and gratuities, and any no-show or quantity change provisions. This allows for accurate pre-payment by the guests. The organizer should also make it clear to all guests what your (the organizer's) cancelation and no-show policy is (including total forfeiture warning if applicable).
Most important in my experience is to make it clear to the restaurant or hotel when negotiating that this is a "no-host" event and guests will be pre-paying the exact amount to the organizer. Many restaurants and hotels sometimes assume there is a company pickeing up the tab and aren't too worried about slop. You don't want any surprises or hidden charges that you would have to pay for out of your own pocket. So communicate well with the property just what your event is.
In the event where the above was not followed, or somebody skips out without paying their bar tab, then it's always going to be a punt situation with some stress. Not much you can do about that, and you just have to work out things as best as you can.
Ultimatly however, it's the organizer's (the person who arranged things or was the "contact person" for the restaurant) final responsiblity.
If you decide to allow a "late comer" who doesn't have time to get their payment into you in advance, it must be made clear to them that if they don't show, they still may have to pay. If the person doesn't pay or drops off the face of the planet, I would say it's up to the organizer to foot the bill. They "approved" this person, after all.
[This message has been edited by PremEx (edited 09-07-2001).]