It means that the three auction houses have moved from matching charges for buyers in their main categories to operating three separate systems.
Although all three use a staggered premium rating of 25%/20%/12%, they have all now adopted differing thresholds at which those percentages change.
Sotheby's chose to push their thresholds to a higher level than those announced by Christie's at the end of last month.
Bonhams' chief executive for the UK and Europe, Matthew Girling, said: "With the USA just coming out of recession and Europe still struggling, we do not feel this is the right time to be adding to our buyers' costs by increasing the buyers' premium thresholds."
