Ticketmaster GmbH is not organizing any of these events, but is contracted by the event promoters to sell tickets. The event promoters generally don't accept any return or trade requests. You are clearly informed about the liability of the tickets while ordering them.
Please note, that simple ticket orders are exempt from the distance selling law. This is because sports, leisure, and cultural events can't be organized logistically and financially with a two week return period. The legislation sees this the same way, which is why the law doesn't apply when you create a contract with the event promoters for the completion of a service in the area of recreational activities (§ 312 b par. 3 No.6 German Civil law).