Site re-selling tickets for a higher price then original (Very similar to black market sales of tickets).
This is illegal in some countries, and they have no refund policy.
No guarantee that you are the only one having the given ticket they sell. Bought a ticket, but couldn't access the concert, as somebody else already where there.
Fake Tickets / Counterfeits / kein wirklicher Ticketverkauf. Infos in der Tagespresse:
siehe auch: viagogo.de / viagogo.co.uk
Das Unternehmen hat auch keine echte Anschrift!