Regarding the above example:  
 
 The extra £2643.75 the buyer pays is only part of the story.  The auction house then takes almost as much again from the seller.  This means he - the seller - receives only approx. £13000 of the £15000 hammer price.  The auction house itself takes the remainder - meaning it makes approx. £5000 from the sale!
 
 What do they actually DO to earn such huge commission?  Polish the paintwork?