On their faq they say:
Jumbo Ticket is a secured and certified site which is probably fair. Jumbo Ticket strives for 100% customer satisfaction.
But we can't find any certification link on the site.
Great point. I think Jumbo Ticket must consider being fair and transparent in every steps. I would also recommend this and along with this, also, picking the winner should be transparent in a way which can be verified by anyone through online.