Unfortunately you can find tickets on sale outside the official market. Ill-intentioned people buy numerous tickets in order to propose them in the resale at exorbitant prices. Those practices are unacceptable and you could be the victims.
We know that we can’t prevent you from buying those. However you would be the first victims. Besides the high price you would pay, nothing can guarantee the validity of those tickets. The admission could be refused. Choose the official networks in order to pay the right price and to be assured of your admission on the festival ground.