If you ever been unsure about leaving an absentee bid with an auction house your concern is justified. There are two ways to leave an absentee bid: 1. Place an absentee bid directly with an auction house, or 2. Place an absentee bid with a third party online bidding platform such as Interencheres, Drouot Live, Invaluable, Live Auctioneers, The Saleroom or Bidsquare.
Placing an absentee bid directly with an auction house in France is courting disaster. My experience, is that even if the live bidding realizes an auction price lower than your absentee bid the auction house will invoice you for one bid increment less than your absentee bid. For example, if you place an absentee bid for 1500 Euros for a Daum vase and the final bid onsite is 900 Euros, the auction house will invoice you for 1400 Euros plus their commission fee. Unfortunately this has happened repeatedly to me and confirmed by my French friends overseas.
My recommendation is do not place absentee bids directly with an auction house unless they confirm how absentee bids are processed.
An option is to place an absentee bid with a third party online bidding platform. This is a better option because “in most cases” the absentee bid is confidential and is not shared with the auction house. The exception that I am aware of is that an absentee bid placed on Drouot Live is shared with the auction house.