Here's how the bid deposits work on the Timechain Artifacts website auctions.
When placing a bid, if the deposit popup comes up, you have 2 options;
1. One deposit for unlimited bids
2. Smaller incremental deposits that allow unlimited bidding but only up to a specific amount. (for example a deposit of 0.0025 BTC would allow you to make unlimited bids up to 0.35 BTC, so it's about 0.75 - 3% of the bid amount. To make bids higher than 0.35 BTC you would make another incremental deposit.
If your incremental deposits reach the same value as the one-time unlimited bid deposit amount, your bidding will no longer have an upper threshold and you can make bids as high as you'd like without further deposits.
If you win the auction, you only need to pay the balance due after your deposits.
If you don't win the auction, deposits are refunded within 48 hours of the auction close.
Winning bidders get 48 hours to make payment on their auctions. If the winning bidder does not complete payment within that time, the item is awarded to the 2nd highest bidder and the deposit would be forfeit.
If you have any questions about bid deposits, please email me at FractalEncrypt@TimechainArtifacts.com or you can DM me on Twitter for a quicker response.