Ticketmaster has a monopoly on ticket sales in the US. Some bands have tried to go around them (PearlJam) but have mostly lost.

Ticketmaster cannot stop computer bots from manipulating their systems. Ticket brokers have software that purchases all the tickets the instant that they go on sale. Ticketmaster cannot stop them and honestly has no incentive to, as they do not care who buys the tickets.

Here is an article on it.

http://www.denverpost.com/familynews/ci_7185798