Actually deputy services justify their charges as 
they run the risk when their offshore bidders 
don't pay up.

They've entered into binding sale & purchase 
contracts with the seller and they have to pay 
up - regardless of whether you as the real bidder 
pays or not.

I think 20% is a reasonable premium for bidding 
for someone else whom you've never seen and run 
settlement risk. 

Maybe if you've put through 10  transactions then 
you could argue for a price reduction - remember 
he doesn't have credit check on you!