Online auction
I recently attended an auction in person that was listed on "The Saleroom", the auction house I visted had a webcam and microphone set up on the auctioneer and they were taking live bids through the internet as the auction went along, with the auctioneers keeping an eye on the screen and on the room.
I'm no expert and maybe different auction houses have different arrangements, at this auction there was a 15% buyers premium on the hammer price, with VAT to be paid on the buyers premium, i.e. £100 hammer price, £15 buyers premium, £3 VAT on the £15 = £118 total cost.
And there was also 3% to be added if bidding online, but I'm not sure at which point that was added to the total.
It was my first auction, very interesting, although nerve racking as higher bids kept coming through online. You could tell when people in the room had reached their limit, but had no clue when the bids would dry up online.
Usually if you click on the Saleroom link through to the auction house's own website, they will list all their terms, premiums etc.