It is also possible that a TA is posting online prices that he just "didn't get around to updating yet." - There is always a permissable time lag because prices change so quickly.
Also lately I saw that Revelex (A big technology company that has a cruise sales software engine for independent cruise sellers online) had a system where they updated prices every morning, and it would always (automatically) grab the lowest price it saw in any category.
For some Princess (I believe) cruises it was picking up the 50%-off third person in a cabin price and displaying that as the retail price in a certain category. Obviously just an outright error. I read soon after that Revelex had fixed this bug. And this was only a few months ago.