Tickets are non-refundable. We're fine with transfers though, provided you don't charge more than you paid. Just email tickets@nineworlds.co.uk with 1) your name and email, and 2) the name and email address of the new ticket holder.
To find someone to buy your ticket, try tweeting and including @london_geekfest in your tweet so we can RT, and also posting in the Facebook Ticket Resale group.