Both Copart and IAA let you leave a proxy (pre-bid) or bid live. The mechanics matter:
- A proxy executes incrementally, so you rarely pay your ceiling — but it also commits you before sale-day announcements are read.
- Live bidding lets you react to last-minute announcements, at the cost of auction-floor adrenaline.
- On dealer platforms like Manheim, proxy behavior interacts with floor prices set by sellers — an unmet floor turns your “win” into an “if” sale pending seller approval.
Our suggestion for new buyers of used cars at auction: proxy at your written maximum, then leave the laptop. You remove the emotion, which is the house's main edge.