Face price: what the agency paid for the ticket
[*]
Booking fee: what pays for their staff, premises, IT systems, credit card transaction fees, ...
If you don't like it, buy direct from the venue. If you can, because many venues have realised that running a box office is actually quite expensive (probably for all the above reasons) and would rather not deal with the public direct
There's a case for rejigging the way prices are presented so that the agency margin is inside the face price not outside it, but until that happens the booking fee is not going away
[*] actually it's worse than that. See e.g.
http://www.authoritytickets.com/?p=128