Cost of reselling tickets?

This might be a broader question on Ticketmaster and not specific to this Radiohead tour - I'm in the UK and got a Copenhagen code, so I'm going to try to get x4 tickets for Copenhagen tomorrow...

Were one of my friends who received a London code successful in getting 4x tickets, would there be any cost to me in just reselling the Copenhagen tickets back to Ticketmaster? And how much typically?