I understand your frustration, but I'm going to bet you don't know the reason for said dealer's tardiness. There could have been a personal emergency or something that was out of their control keeping them from arriving on time. No con that I can think of would 'ban' someone just because they were late arriving to their selected spot. A guest was late to a panel today and stalled said panel for about, oh, 7 minutes. Should they be banned to appease those who had to wait? No.
That being said; I do not understand delaying opening the marketplace because some dealers were late... those dealers lose out on money if they can't sell product. On the flip side, perhaps the thought was that since some dealers were late, their booths would be unattended and the rare nefarious brony would swipe something when no one is looking; and there is not enough security the con has to watch every single booth, so the simplest solution was to give them some time to arrive before opening the doors.
The above is speculation only, as I am not on staff; but it would make sense to me, and I second the notion: you don't like a way something is done; offer to help rather than just complain.