Only buy from the top agencies, Ticketmaster, See Tickets, Ents24, Live Nation, TicketWeb, or from the venue box office.
Agencies like getmein.com charge the earth for tickets, they basically get people to buy up tickets on their behalf, then sell them for extortionate amounts of money, not far off touting, in my opinion. If you intend going to more concerts, and I go to as many as I can afford, then it’s worth checking out the artists Facebook page, or other online presence, and ‘Liking’ them, you will often get advance fan ticket sales, sometimes several days in advance, which happened with the Arcade Fire tickets a month or so ago.
Then get to the venue early, if you have unreserved tickets; arriving late, then shoving to the front really pisses off other people!