I just watched a video 
Many people think that the old British money system £ s d (Pounds,shillings,pence) was unnecessarily complicated, but it was set up that way for a reason which made the arithmetic really easy.
Each pound was divided into 20 shillings and each shilling was divided into 12 pence.
Retail items were often sold in Dozens (12) and priced in shillings. Thus if the price was 2 shillings per dozen the price per item was 2d (pence). Trade or bulk items were sold in tons which subdivided into 20 cwt (hundredweight) and these stocks were usually priced in £ (pounds) so if the price of wheat was £16 a ton, the price of a cwt of wheat was 16s (sometimes written 16/-).
Another interesting item of currency was the guinea which was 21s or £1 1s.
Auctions were priced in guineas which is what the buyer paid, but the seller was paid the number of guineas in pounds and the residue was kept by the auctioneer as his commission. So if the bidding on your horse ended at 25 guineas the buyer paid £26 5s and you got £25. The auctioneer kept 25s or £1 5s. This amounts to a commission of 5% which was very reasonable by today's standards.
Auctioneers today charge a buyer's premium of 15-20% over the hammer price AND deduct 15% selling commission as well. So if an item sells for £100, the buyer pays £100+£20(BP)+£4(VAT)=£124 and the seller gets £100-£15(SC)-£3(VAT)= £82. That is a difference of £42 between what the buyer pays and the seller receives. £35 (35%) going to the auctioneer and £7 to the government as VAT.
If you said that today's auctioneer system was extortionate, I would have to agree, but that is where we have got to and the only way it will change is if people stop using auctioneers to sell their goods.