[Police] For a show sold out

I saw this posted a while ago, but I am just getting around to reading it now. Somebody said...

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Look at it from the ticket agents point of view - if everyone thinks the shows are sold out, they can bump up the price of tickets they have spare because of the hysteria factor and that ultimately, human nature makes it compulsive for people to want to get in to a show that's full....<<

The ticket prices were set long before any went on sale, weren't they? Gary